UC-NRLF 


ANNALS  OF  THE  NEW  YORK  ACADEMY  OF  SCIENCES 
Vol.  XXII,  pp.  161-224 


Editor,  EDMUND  OTIS  HOVEY 


METAMORPHISM  OF  PORTLAND  CEMENT 


BY 

ALBERT  B.  P  ACINI 


NEW  YORK 
PUBLISHED  BY  THE  ACADEMY 

10  SEPTEMBER,  1912 


X 


N    sO 


THE  NEW  YOEK  ACADEMY  OF  SCIENCES 
(LYCEUM  OF  NATURAL  HISTORY,  1817-1876) 


OFFICERS,  1912 

President — EMERSON  McMiLLiN,  40  Wall  Street 
Vice-Presidents — J.  EDMUND  WOODMAN,  FREDERIC  A.  LUCAS, 

CHARLES  LANE  POOR,  E.  S.  WOODWORTH 

Corresponding  Secretary — HENRY  E.  CRAMPTON,  American  Museum 
Recording  Secretary — EDMUND  OTIS  HOVEY,  American  Museum 
treasurer — HENRY  L.  DOHERTY,  60  Wall  Street 
Librarian — EALPH  W.  TOWER,  American  Museum 
Editor — EDMUND  OTIS  HOVEY,  American  Museum 

SECTION  OF  GEOLOGY  AND  MINERALOGY 

Chairman — J.  E.  WOODMAN,  N.  Y.  University 
Secretary — CHARLES  P.  BERKEY    Columbia  University 

SECTION  OF  BIOLOGY 

Chairman — FREDERIC  A.  LUCAS,  American  Museum 
Secretary — WILLIAM  K.  GREGORY,  American  Museum 

SECTION  OF  ASTRONOMY,  PHYSICS  AND  CHEMISTRY 

Chairman — CHARLES  LANE  POOR,  Columbia  University 
Secretary — F.  M.  PEDERSEN,  College  of  the  City  of  New  York 

SECTION  OF  ANTHROPOLOGY  AND  PSYCHOLOGY 

Chairman — K.  S.  WOODWORTH,  Columbia  University 
Secretary— FREDERIC  LYMAN  WELLS,  Columbia  University 


The  sessions  of  the  Academy  are  held  on  Monday  evenings  at  8:15 
o'clock  from  October  to  May,  inclusive,  at  the  American  Museum  of 
Natural  History,  77th  Street  and  Central  Park,  West. 


[ANNALS  N.  Y.  ACAD.  Sci.,  Vol.  XXII,  pp.  101-224.     10  September,  1912] 

METAMOEPHISM  OF  PORTLAND  CEMENT  l 
%  BY  ALBERT  B.  PACINI 

(Read  before  the  Academy,  Part  I  on  8  January,  1912;  Part  II,  1  April, 

1912) 

CONTENTS 

PART  I  rage 

Introduction 102 

Nature  of  the  problem 163" 

Chemical  composition 104 

Mineralogical  constitution 165 

Setting  process 165 \ 

Hardening  process 166 

Influence  of  water  upon  metainorphisin 168 

Temperature  of  the  water  at  first  added "169* 

Temperature  of  the  water  that  may  subsequently  come  into  contact 

with  the  system 171 

Quantity  of  water  at  first  added 172 

Size  of  cement  particles 172 

Laitance 1 7:> 

Hydrolysis  theory 1 74 

Mechanical  agitation  when  water  is  added 174 

Total  quantity  of  water  at  first  added 175, 

Quantity  of  water  that  may  subsequently  come  into  contact  with  the 

system 175" 

Surface  treatments 177 

Membranes 177 

Mass  treatments 177 

Quality  of  water  at  first  added 178 

Having  material  in  solution 178 

Quality  of  water  that  may  subsequently  come  into  contact  with  the 

system ISO 

Having  material  in  solution ISO 

Sea   water 180 

Alkali  and  deep  rock  waters 181 

Having  material  in  suspension .  185 


1  A   thesis  submitted  in  candidacy  for  the  degree  of  Doctor  of  Science  at  New  York 
University,  1912. 

Acknowledgments  are  due  to  Prof.  .7.  Edmund  Woodman  and  Mr.  Raymond  B.  Earler 
of  the  Department  of  Geology,  New  York  University,  and  to  Engineer  Inspector  Ernst 
Jonson,  Board  of  Water  Supply,  City  of  New  York,  for  valuable  suggestions  made  dur- 
ing the  preparation  of  this  paper  ;  also  to  Mr.  Fred  H.  Parsons,  Assistant  Engineer,  and 
Messrs.  James  E.  Jay,  Charles  M.  Montgomery  and  Charles  E.  Price,  Inspectors,  of  the 
Board  of  Water  Supply  Laboratory,  for  material  assistance  during  the  experimental 
work. 

(161) 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

PART  II 

Page 

Experimental  investigation 184 

Temperature  of  the  water  at  first  added 18<j 

Temperature  of  the  water  that  may  subsequently  come  into  contact 

with  the  system ; 180 

High-pressure  steam 18G 

Cold  storage : 187 

Quantity  of  water  at  first  added 18!) 

Size  of  cement  particles 180 

Mechanical  agitation  when  water  is  added 191 

I          Setting  time  of  cement  in  laboratory  air  and  in  damp  closet 192 

Effect  of  excess  of  mixing  water  on  strength  of  concrete 193 

Effect  of  excess  of  mixing  water  on  permeability  of  concrete 194 

••  Effect  of  excess  of  mixing  water  on  strength  of  neat  cement 195 

Effect  of  the  presence  of  clay  and  dissolved  substances 198 

Quantity  of  water  that  may  subsequently  come  into  contact  with  the 

system 200 

Permeability 200 

Concretes  containing  different  aggregates 204 

Concretes  containing  different  cements 205 

Effect  of  the  direction  of  flow  through  concrete 20(3 

Quality  of  water  at  first  added 208 

Compressive  strength  of  neat  cements  gaged  with  various  solutions  208 
'          Effect    of   gaging   with    various    solutions   upon    the    strength    of 

i  mortars  afterward  stored  in  water 210 

Effect  of  gaging  grout  with  rock  waters 211 

Quality  of  water  that  may  subsequently  come  into  contact  with  the 

system 213 

Theoretical  considerations 213 

Effect  of  storage  in  various  saline  solutions  upon  the  strength  of 

mortar 214 

Effect  of  storage  in  rock  water  upon  the  strength  of  lean  cement 

mortars 216 

Summary  of  experimental  results 218 

General  conclusions 219 

Bibliography 220 


PART  I 

INTRODUCTION 

The  important  field  of  investigation  covering  the  changes  which  take 
place  in  the  setting  and  hardening  of  Portland  cement  and  in  Portland 
cement  which  may  be  considered  to  have  attained  the  greater  part  of  its 
maximum  hardness  calls  for  the  services  of  experts  in  various  branches 
of  science.  Many  of  the  general  problems  can,  as  a  whole,  be  relegated 


i,   METAMORPHISM    OF   PORTLAND   CEMENT  163 

to  the  petrologist  and  hydrologist ;  and  this  paper  is  an  attempt  to  treat 
cement  as  a  rock,  differing  from  other  rocks  only  in  being  artificial,  but 
subject  to  the  same  internal  and  external  influences  as  other  components 

of  the  earth's  crust. 

% 

A  training  in  geophysics  and  geochemistry  is,  perhaps,  the  most  valu- 
able asset  in  surveying  the  field  of  Portland  cement.  If  no  other  end  is 
achieved  by  the  following  pages,  the  mere  representation  of  the  question 
as  a  problem  in  applied  petrology  will,  it  is  hoped,  help  future  investi- 
gators in  a  more  systematic  inquiry. 

Part  I  of  this  paper  is  devoted  to  a  necessarily  brief  review  of  the 
present  status  of  the  subject,  and  no  attempt  is  made  to  discuss  data 
quantitatively.  Experimental  results  in  elaboration  of  the  various  points 
discussed  are  presented  in  Part  II. 

The  experiments  described  in  Part  II  were  made  at  the  laboratory  of 
the  Xew  York  Board  of  Water  Supply  by  the  writer,  and  in  part  by  his 
associates,  in  the  course  of  the  investigations  of  the  Board.  The  most 
modern  and  complete  equipment  was  available,  thanks  to  the  prudent 
foresight  of  the  gentlemen  at  the  head  of  this  great  engineering  enter- 
prise. The  data  are  reproduced  by  permission  from  the  periodical  bulle- 
tins of  the  Inspection  division  and  from  the  annual  report  of  the  Board 
for  1911. 

XATURE  OF  THE  PROBLEM 

Portland  cement  is  a  finely  ground  artificial  rock,  whose  essential 
constituents  are  silica,  alumina  and  lime.  In  it  are  found  a  number  of 
component  minerals  recognizable  by  definite  optical  properties,  but  the 
individual  constitution  of  which  is  not  yet  clear.  The  percentages  of 
these  minerals  vary  somewhat  according  to  the  method  of  manufacture 
and  the  purity  of  the  raw  materials,  but  there  is,  on  the  whole,  a  fairly 
stable  proportion  in  a  series  of  normal  cements. 

The  method  of  manufacture  of  Portland  cement  will  not  be  discussed 
here  further  than  to  state  that  it  consists  essentially  of  the  calcination 
of  a  mixture  of  calcareous  and  argillaceous  rocks  at  high  temperatures. 
Usually,  about  2  per  cent  of  gypsum  or  of  plaster  of  Paris  is  afterwards 
added  to  retard  the  set.  By  varying  the  proportion  of  these  rocks,  the 
temperature  and  duration  of  calcination,  the  fineness  of  grinding,  and 
also  by  the  addition  of  foreign  substances  products  are  obtained  having  a 
wide  range  of  hydraulic  properties. 

The  hydraulic  properties  are  setting  and  hardening.  Setting  is  the 
attainment  of  rigidity  by  the  plastic  mixture  of  cement  and  water  and 
begins  immediately  after  mixing,  requiring  several  hours  for  completion. 


164  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

Hardening  is  the  progressive  increase  in  strength  acquired  by  the  mass, 
and  it  attains  the  greater  part  of  its  ultimate  value  in  about  a  year. 
Even  after  this  period  it  is  subject  to  a  small  progressive  increase  (42 )2. 
In  general  the  properties  of  setting  cement  are  to  be  found  both  in 
mortars,  or  mixtures  of  cement  and  sand,  and  in  concretes,  or  mixtures 
of  cement,  sand  and  broken  stone,  these  chemically  inert  materials  added 
to  the  cement  exerting  a  physical  influnce  on  metamorphism. 

CHEMICAL  COMPOSITION 

The  chemical  composition  of  normal  Portland  cement  is  shown  in  the 
following  tables : 

Avcrayc  of  300  Normal  American  Portland  Cements,  Representing  20  Vraml* 

of  AH  Types 

(Analyses  by  the  writer  for  the  Board  of  Water  Supply) 


A1,0S 
CaO 
MgO 
SO3 


Average  of  100  German  Portland  Cements 
(Burchartz,   (12)  ) 

SiO 20.87 

Fe,O;.   2 . 98 

ALO.," 7 . 63 

CaO   02 . 99 

MgO    1 .55 

SO3 1 . 85 

The  ultimate  chemical  composition  of  a  cement  is  only,  however,  a 
rather  indirect  clue  to  its  hydraulic  properties,  just  as  the  ultimate 
analysis  of  a  composite  rock  may  only  give  a  faint  idea  as  to  its  con- 
stituent minerals  or  possible  products  of  metamorphism.  For  example, 
it  would  be  quite  possible  to  synthesize  a  mixture  which  would,  on  analy- 
sis,, correspond  exactly  to  the  chemical  composition  of  an  excellent  Port- 
land cement,  yet  which,  when  gaged  with  water  in  the  ordinary  way, 
would  develop  practically  no  tensile  strength,  in  fact  would  possibly  fail 
to  set  at  all. 

Cement,  therefore,  must  owe  its  hydraulic  possibilities  to  a  particular 
grouping  of  its  constituent  compounds,  quite  analogous  to  a  series  of 


Maximum 
25  89 

Minimum 
19.85 

Average 

22  70 

4  .  OS 

1  23 

2  73 

010 

3  43 

6  17 

04.01 

59  .  06 

O9  07 

4  00 

0  30 

2  19 

1  75 

0  84 

1  37 

H,O.  alkalies... 

2.17 

2  Numbers  in  parentheses  refer  to  the  bibliography  at  the  end  of  this  article. 


P ACINI,   METAMORPHISM    OF   PORTLAND    CEMENT  165 

minerals;  and  looking  to  the  identification  and  classification  of  these 
minerals,  a  great  deal  of  investigation  has  been  done. 

By  trial  burnings  of  simplified  mixtures,  such  as  lime-silica  melts,  and 
by  microscopical  examination  of  sections  of  the  resulting  clinker,  the 
problem  ts  gradually  being  clarified,  but,  owing  to  its  great  complexity, 
much  controversial  literature  thereon  has  been  issued  on  both  sides  of 
the  Atlantic  (52,  69,  80,  64,  65,  88).  The  theories  put  forth  have  so  far 
had  little  practical  effect  upon  the  manufacture  and  composition  of  the 
commercial  product  (63). 

No  complete  and  final  enumeration  of  the  chemical  compounds  result- 
ing from  the  burning  of  such  a  mixture  of  clay  and  limestone  has  yet 
been  accepted  as  authoritative.  The  microscopical  identification  of  the 
individual  chemical  compounds  which  go  to  make  up  the  mineralogical 
entities  is  at  best  somewhat  unsatisfactory,  especially  because  of  the 
minuteness  of  the  particles  of  raw  materials  necessary  to  secure  thorough 
and  uniform  calcination,  and  consequently  the  extremely  small  size  of 
the  resulting  crystals  and  aggregates.  It  has  been  proposed,  in  this  con- 
nection, to  secure  these  of  a  size  available  for  study  by  the  expedient  of 
fusing  the  clinker  in  an  electric  furnace;  and,  by  this  means,  a  partial 
clarification  of  the  system  has  been  obtained  (103). 

MINERALOGICAL  CONSTITUTION 

The  minerals  which  are  recognized  in  cement  clinker  have  been  named 
alit,  belit,  felit  and  celit  (101),  and  a  metamorphism3  of  these  occasioned 
by  the  action  of  water  is  the  cause  of  the  setting  and  hardening  of  Port- 
land cement. 

Alit  has  been  reported  a  solid  solution  of  tri-calcic  silicate  in  tri-calcic 
aluminate,  and  celit  a  solution  of  di-calcic  aluminate  in  di-calcic  silicate 
(61).  Other  investigators  have  reported  alit  and  celit  to  be  silicates  of 
different  silicic  acids  (26). 

Belit  is  probably  a  calcium  aluminum  silicate  of  the  composition 
Ca3Al2Si2010,  a  form  found  in  nature  as  the  mineral  gehlenite  (27). 

SETTING  PROCESS 

Precisely  what  chemical  reactions  and  physical  transformations  take 
place  in  the  setting  and  hardening  processes  is  not  yet  definitely  settled. 
It  may,  however,  be  stated  that  by  modifying  the  proportions  of  clay  to 
limestone  through  a  certain  range,  we  obtain  a  product  which  varies  in 
its  speed  of  setting  and  of  hardening.  In  general,  cements  high  in  silica 

3  Metamorphism  :  Any  change  in  the  constitution  of  any  kind  of  rock,  Van  Hise  (104). 


166  AXXALS  XEW  YORK  ACADEMY  OF  SCIENCES 

are  found  slow  setting  and  slow  hardening,  while  those  high  in  alumina 
are  quick  setting  and  quick  hardening.  An  increase  of  lime  in  the  latter 
retards  the  setting  (63). 

The  calcium  aluminates  are  probably  the  main  factors  in  the  setting 
of  cement,  while  the  hardening  is  due  to  the  calcium  silicates.  The  mag- 
nesium compounds  are  inessential  to  the  hydraulic  processes  (105). 

Upon  the  addition  of  water  to  cement,  the  equilibrium  in  the  system 
of  solid  solutions  and  chemical  compounds  is  destroyed,  and  a  series  of 
changes  is  inaugurated  tending  towards  the  production  of  a  system  which 
will  be  stable  under  the  new  conditions.  The  first  effect  resulting  from 
the  solutions  and  reactions  brought  about  by  the  presence  of  water  is  the 
setting  of  the  plastic  mass. 

Under  ordinary  conditions  of  practise,  the  quantity  of  water  used  is 
about  22  per  cent  in  the  case  of  a  neat  cement,  being  less  in  the  case  of  a 
mortar,  and  still  less  in  the  case  of  a  concrete.  When  this  proportion  of 
water  is  used,  it  is  probable  that  the  setting  of  cement  is  mechanically 
analogous  to  the  setting  of  plaster  of  Paris  and  is  caused  by  the  growth 
throughout  the  mass  of  a  network  of  crystals,  deposited  from  the  satu- 
rated solution  formed  by  the  first  stage  of  hydro-nietamorphism. 

Owing  to  the  lo\v  solubility  in  water  of  the  original  component  sub- 
stances, the  attainment  of  final  equilibrium  is  a  matter  of  considerable 
time,  and  is  further  delayed  by  the  automatic  protective  action  of  films 
of  insoluble  substances  coating  the  active  particles  (23).  These  films  in 
some  cases  are  semi-permeable,  and  exert  a  selective  influence  upon  the 
solutions  osmotic-ally  penetrating  them.  Under  normal  conditions,  that 
is  under  those  conditions  which  have  been  found  in  practise  to  yield  the 
densest  and  strongest  product,  this  attainment  of  equilibrium  considered 
apart  from  the  setting  process  at  first  proceeds  rapidly,  but  the  rate  of 
increase  of  strength  grows  smaller,  tending  to  a  minimum. 

A.  Erskine  Smith  has  shown  (90)  that  there  has  been  no  permanent 
retrogression  in  the  strength  of  cement  in  the  case  of  specimens  kept 
under  observation  for  21  years.  Of  course,  this  relates  to  laboratory 
specimens  protected  from  weathering,  but  shows  one  of  the  directions 
which  this  met  amor  phi  sm  may  take. 

HATJDEXIXG  PROCESS 

The  hardening  of  cement  has  been  ascribed  variously  (-±8) 

1.  To  the  fineness  of  grinding, 

2.  To  the  increasing  stability  of  calcium  compounds  due  to  combina- 
tion of  part  of  the  silicic  acid  as  the  silicates  grow  less  basic, 

3.  To  the  action  of  free  lime  upon  calcium  compounds, 


P ACINI,   METAMORPHISM    OF  PORTLAND   CEMENT  167 

4.  To  the  decomposition  of  basic  products  present  in  the  freshly  set 
cement, 

5.  To  equilibrium  of  calcium  hydroxide  with  the  siliceous  constitu- 
ents, and 

6.  To  the  hydration  of  the  double  silicates  and  anhydrides  of  lime  and 
alumina. 

The  two  theories  that  have  at  present  the  greatest  claim  upon  con- 
sideration are  that  the  strength  of  set  cement  is  due  to  the  progressive 
crystallization  of  calcium  hydroxide  (80),  and,  in  some  respects  diamet- 
rically opposed,  that  this  strength  is  due  to  the  formation  of  a  dense 
complex  colloid,  soft  at  first  but  gradually  adsorbing  calcium  hydroxide 
and  thus  becoming  harder  and  harder  (64,  65). 

According  to  the  latter  theory,  cement  consists  of  a  mixture  of  fused 
compounds  of  silicic,  aluminic  and  ferric  acids  with  lime,  together  with 
an  excess  of  lime,  partly  dissolved  and  partly  enclosed.  Upon  the  addi- 
tion of  water  to  this  system  it  is  decomposed,  and  the  water  becomes  a 
supersaturated  solution  of  salts,  which  react  between  themselves.  The 
compounds  resulting  from  these  reactions  crystallize  about  the  cement 
grains  in  needle-shaped  crystals.  So  far,  the  process  is  analogous  to  the 
setting  of  plaster  of  Paris  (45),  and  silica  takes  no  part  in  these  pre- 
liminary reactions. 

A  hydrogel  begins  to  form  about  each  grain,  in  which  the  crystals 
become  embedded.  This  hydrogel  consists  essentially  of  calcium  hydro- 
silicate,  and  to  a  minor  degree  of  calcium  hydroaluminate  and  calcium 
hydroferrite.  At  first  it  is  soft  and  plastic,  but  gradually  becomes  dense 
and  rigid  by  the  adsorption  of  calcium  hydroxide.  The  strength  of 
cement  is  mainly  due  to  this  process  of  coagulation. 

The  calcium  hydroxide  may  of  course  crystallize  and  lend  additional 
strength;  but  its  crystallization  is  rather  more  likely  to  burst  the  har- 
dened cell  walls  about  each  grain  of  cement,  and  thus  admit  liquids 
later  in  the  process  which  may  be  fatal  to  the  integrity  of  the  structure, 
either  by  undesirable  chemical  reactions,  or  simply  by  dissolving  away 
the  lime,  with  the  formation  of  soft  hydrates  of  silica,  alumina  and  iron 
oxide,  instead  of  the  desired  hardened  colloid  (64,  65). 

Much  corroborative  evidence  has  been  offered  by  supporters  of  this 
view,  and  similarly  by  the  exponents  of  the  crystallization  theory  in 
defense  of  that.  The  question  is  still  at  issue,  and  the  main  difficulty  is 
the  microscopic  recognition  of  the  constituents  of  set  cement  (34,  78). 
Unquestionably,  colloidal  materials  result  from  the  action  of  water  on 
silicates  of  this  type,  when  the  particles  have  been  ground  to  the  fineness 
of  Portland  cement  (23,  21,  95).  This  has  been  directly  observed  in  the 


168  ANNALS  XEW  YORK  ACADEMY  OF  SCIENCES 

case  of  cement  and  reproduced  with  synthetic  mixtures.  What  binding 
power  colloidal  material  may  develop  is  strikingly  seen  in  the  case  of 
conglomerates  and  sandstones  in  which  hydrous  silicic  acid,  aluminic 
hydroxide  or  ferric  hydroxide  has  been  the  cementing  material,  so  that 
the  theory  is  attended  by  a  high  degree  of  probability. 

On  the  other  hand,  it  is  also  quite  conceivable  that  the  interlocking  of 
crystalline  masses  between  the  grains  of  cement  may  account  in  some 
measure  for  the  strength.  There  is  definite  evidence  that  calcium  hy- 
droxide does  crystallize,  and  its  mineralogical  and  crystallographic  con- 
stants have  been  determined  (24). 

The  two  views  are  not  entirely  irreconcilable,  and  it  is  possible  and 
even  probable  that,  mechanically,  the  strength  of  cement  acquired  by 
hardening  is  due  to  both  processes.  Whatever  be  the  chemical  reactions 
in  detail  by  which  these  elements  of  the  structure  are  produced,  the  main 
condition  for  their  occurrence  is  the  presence  of  water. 

This  paper  is  devoted  to  an  enumeration  of  the  factors  which  influence 
the  metamorphism  caused  by  water  in  Portland  cement,  and  the  varia- 
tions in  the  physical  properties  of  the  resulting  rock,  brought  about  by 
varying  these  factors. 

IXFLUEXCE  OF  WATER  UPOX  METAMOKPIIISM 
The  action  of  water  upon  Portland  cement  is  a  resultant  of 

1.  The  temperature  of  the  water 

A.  At  first  added 

B.  That  may  subsequently  come  into  contact  with  the  system 

2.  The  quantity  of  water 

A.  At  first  added  4 

a.  Size  of  cement  particles 

b.  Mechanical  agitation  when  water  is  added 

c.  Total  water  added 

B.  That  may  subsequently  come  into  contact  with  the  system 

3.  The  quality  of  water 

A.  At  first  added 

a.  Having  material  in  solution 

B.  That  may  subsequently  come  into  contact  with  the  system 

a.  Having  material  in  solution 

b.  Having  material  in  suspension 

4  Owing  to  the  peculiar  autoprotective  reaction  of  cement  against  the  action  of  water, 
before  alluded  to,  the  quantity  of  water  coming  into  contact  with  cement  is  a  function 
of  the  size  of  the  particles  and  of  mechanical  stripping  of  protective  films,  as  well  as  of 
the  ratio  of  cement  to  water. 


PAC1NI,   METAMORPHISM   OF  PORTLAND   CEMENT  159 

The  final  effects  of  geological  processes  do  not  differ  in  the  main, 
whether  these  operate  upon  natural  substances  or  upon  the  products  of 
human  industry.  The  agent  whose  activity  is  responsible  for  the  majority 
of  terrestrial  changes,  namely  water,  is  also  the  main  factor  in  the  meta- 
morphism^of  the  artificial  rock,  cement.  By  intelligent  control  of  the 
action  of  water  upon  this  rock,  the  desired  results  are  obtained,  and  its 
value  as  a  material  of  construction  is  inestimable.  Lacking  this  insight, 
the  action  of  water  may  result  in  catastrophe,  or  at  least  loss  of  time, 
money  or  efficiency.  Geology,  then,  through  hydrology  (59),  is  enabled 
to  give  substantial  aid  to  the  engineer. 

TEMPERATURE    OF    THE   WATER   AT    FIRST   ADDED 

In  construction,  the  water  at  first  added  to  cement,  known  as  the 
gaging  or  mixing  water,  is  subject  to  the  entire  range  of  variation  of 
atmospheric  temperature.  The  lower  limit  is  far  below  the  freezing 
temperature  of  water  and  of  course,  in  this  phase,  water  is  useless  for 
the  purpose. 

Within  the  possible  range  of  temperature  under  working  conditions,  it 
has  been  established  that  as  the  temperature  of  the  gaging  water  used  is 
higher,  the  set  becomes  more  rapid.  Considering  the  setting  due  to  the 
deposition  of  a  network  of  crystals  from  the  supersaturated  mixing 
water,  the  beginning  of  this  deposition  would  be  sooner  attained,  if  the 
water  reached  its  condition  of  supersaturation  more  quickly;  and  this 
condition  would  be  brought  about  by  a  higher  original  temperature, 
provided,  of  course,  that  the  solutes  increased  in  solubility  with  the  tem- 
perature. With  a  higher  temperature,  the  volume  of  the  water  would  be 
greater  and  the  viscosity  less,  and  consequently  its  range  of  activity  would 
be  increased;  that  is,  it  would  be  enabled  to  reach  a  larger  number  of 
cement  particles  and  thereby  more  quickly  arrive  at  its  saturation  point, 
and  the  deposition  of  the  crystalline  network  hastened  in  consequence. 
If  the  temperature  of  the  mixing  water  be  above  about  37°  C.,  the  setting, 
instead  of  being  hastened,  begins  to  be  delayed.  If  the  deposition  of  this 
network  were  a  simple  case  of  precipitation  from  a  hot  solution,  it  would 
be  logical  to  state  that  the  solubility  of  the  compounds  concerned  was  so 
high  at  this  temperature  that  they  were  not  deposited  from  solution. 
The  problem,  however,  seems  chemical  rather  than  physical,  and  it  is 
more  probable  that  this  effect  is  due  to  hydrolysis. 

Hydrolysis  increases  with  the  temperature.  In  the  case  of  the  weak 
salts  that  must  exist  in  the  system  we  have  under  consideration,  the  ulti- 
mate products  of  hydrolysis  are  the  gelatinous  materials — silica,  in  the 
hydrated  form,  aluminic  hydroxide  and  ferric  hydroxide.  The  adsorp- 


170  AXXALS  FEW  YORK  ACADEMY  OF  SCIENCES 

tive  and  coagulative  properties  of  these  materials  unquestionably  do  not 
compare  with  the  coagulative  powers  of  the  complex  colloid  which 
Michaelis  postulates  (64,  65).  If,  therefore,  the  hydration  of  cement 
does  not  proceed  in  a  properly  regulated  manner,  it  is  conceivable  that  it 
may  become  a  hydrolysis,  with  deleterious  effects. 

If  the  mixed  cement  is  allowed  to  freeze,  the  setting  will  not  take 
place,  but  on  thawing  out  the  mass,  setting  is  resumed.  Obviously  the 
transition  of  the  water  to  the  solid  phase  hinders  solution  and  diffusion, 
and  upon  resuming  the  liquid  form,  water  promotes  these  processes  as 
before.  A  slow  setting  has,  however,  been  observed  in  frozen  mixes  (94), 
and  it  is  quite  possible  that  the  phenomenon  of  regelation  may  account 
for  this. 

Smoke  gases  have  been  found  to  have  a  disintegrating  effect  upon 
cement  setting  at  a  temperature  lower  than  7°  C. ;  this  is  attributed  to 
the  formation  at  these  temperatures  of  a  hyd rated  calcium  carbonate, 
having  the  formula  OaCOo,5H20  by  the  action  of  the  carbon  dioxide  of 
the  smoke  gases  upon  the  lime  of  the  cement.  At  slightly  higher  tem- 
peratures this  hydrate  is  transformed  to  pulverulent  calcium  carbonate, 
with  consequent  disintegration  of  the  structure  of  which  it  forms  a  part 
(107). 

The  effects  of  moderate  variations  in  the  temperature  of  the  mixing- 
water  upon  ultimate  strength  are  practically  of  no  great  moment :  even 
mixes  that  have  been  frozen  and  afterwards  allowed  to  resume  their  set 
are  not  materially  affected  in  their  ultimate  strength,  if  the  set  has  not 
proceeded  too  far  at  the  time  of  freezing  (11 ).  More  than  one  repetition 
of  the  freezing  process  upon  the  same  mix,  however,  will  be  quite  de- 
structive to  the  final  hardening. 

If  the  hardening  be  considered  a  process  of  crystallization,  repeated 
freezing  may  be  assumed  to  destroy  the  strength  by  the  formation, 
through  rapid  temperature  changes,  of  relatively  small  and  non-adhesive 
crystals  of  the  calcium  hydroxide  during  the  critical  foundation  period 
of  growth  of  the  crystalline  structure,  so  impeding  and  misdirecting 
consequent  interlocking  that  a  weak  structure  results. 

If,  on  the  other  hand,  the  colloidal  theory  is  adhered  to,  it  is  only 
necessary  to  point  out  that  the  colloidal  cell  walls  about  the  cement 
grains  may  be  ruptured  by  the  expansion  of  the  contained  water  in  freez- 
ing. This  would  result  in  discontinuity  of  the  internal  structure,  and  if 
sufficiently  widespread,  as  would  be  the  case  in  repeated 'freezings,  would 
alone  account  for  weakness. 

Studies  have  been  made  of  the  ultimate  resistance  obtained  from  frozen 
mortars  by  varying  the  amount  of  gaging  water,  with  the  view  of  estab- 


PACINI,   METAMORPHISM    OF   PORTLAND    CEMENT  171 

lishing  whether  "wet"  or  "dry"  mixes  best  resist  the  disruptive  effects  of 
frost  during  setting.  The  results  reported  are  discordant.  An  excess  of 
water  has  been  found  by  one  investigator  to  enhance  the  effects  of  frost 
(85),  while  by  another  it  has  been  found  to  diminish  them  (11).  Theo- 
retically, Mie  disruptive  effects  of  freezing  should  be  enhanced  by  the 
presence  in  the  mass  of  larger  quantities  of  gaging  water.  On  the  other 
hand,  it  can  be  assumed  from  the  colloidal  standpoint  that  an  increase  in 
the  amount  of  water  present  will  result  in  the  formation  of  a  greater 
quantity  of  colloids  and  a  greater  elasticity  of  the  resulting  mass,  to- 
gether with  a  smaller  total  breakage  of  cell-wall  material. 

TEMPERATURE   OF  THE  WATER  THAT  MAY   SUBSEQUENTLY   COME   IXTO 
CONTACT    WITH    THE    SYSTEM 

The  action  of  hot  and  boiling  water  upon  set  cement  is  strongly 
marked  in  the  case  of  cement  which  contains  free  lime,  producing  after 
a  few  hours,  swelling,  distortion  and  cracking  and  even  total  disintegra- 
tion. A  normal  cement  so  treated,  however,  preserves  its  original  form 
and  volume  after  short  periods  of  exposure  to  the  boiling  temperature. 
The  viscosity  of  water  at  high  temperatures  is  greatly  diminished,  and 
the  liquid  is  thereby  enabled  to  penetrate  more  rapidly  the  capillary  and 
subcapillary  voids,  thus  reaching  more  quickly  a  larger  internal  area. 
If,  as  in  the  case  of  an  unsound  cement,  free  lime  is  thereby  reached,  this 
is  slaked  much  sooner  than  it  would  be  under  normal  conditions,  and 
moreover  with  great  violence,  owing  to  the  higher  temperature  of  the 
water,  producing  internal  disruption,  and  perhaps  thus  opening  up  fur- 
ther avenues  to  the  penetration  of  water,  with  a  repetition  of  the  slaking 
process. 

The  boiling  test  here  described  is  a  very  important  one  in  the  testing 
of  cement  for  construction,  but  it  is  perhaps  less  reliable  in  the  case  of 
unsoundness  from  the  presence  of  excess  of  magnesia. 

In  cements  stored  in  waters  of  relatively  high  temperature,  it  is  prob- 
able that  the  processes  of  solution  act  more  rapidly,  from  the  two  reasons 
mentioned  above ;  but  evidence  is  lacking  to  show  that  any  significant 
decrease  in  ultimate  strength  is  thereby  occasioned. 

Data  as  to  the  storing  of  cement  in  waters  of  low  temperature,  yet  not 
subjected  to  the  action  of  frost,  are  not  available  in  the  literature,  but 
they  would  be  interesting. 

In  the  case  of  exposure  to  the  action  of  frost,  the  process  is  quite 
similar  to  that  which  goes  on  in  the  disintegration  of  natural  rocks  and 
depends,  in  like  manner,  upon  the  initial  mechanical  resistance  of  the 


172  AyyALB  XEW  YORK  ACADEMY  OF  SCIEyCES 

mass,  upon  the  total  volume  of  the  voids  and  upon  the  ratio  of  capillary 
to  subcapillary  voids.  The  disruptive  effect  is,  of  course,  due  to  the  ex- 
pansion of  the  water  during  freezing.  Consequently  there  is  a  possibility 
that  during  the  earlier  stages  of  the  history  of  the  mass  this  effect  may 
be  to  a  great  extent  neutralized  by  the  presence  of  soft  colloidal  material 
(45),  because  of  its  lack  of  rigidity. 

Voids  are  undoubtedly  present  even  in  neat  cement  mixes,  and  they 
are  more  common  in  mortars  and  in  concretes;  when,  therefore,  these 
have  attained  a  sufficient  hardness,  they  are  in  all  respects  similar  to  a 
natural  rock  and  subject  to  the  same  katamorphic  processes.  The  effect 
of  frost  increases  in  intensity  as  the  mass  ages  and  loses  elasticity. 

As  water  permeates  the  cement,  even  after  hardening  has  progressed 
to  a  considerable  extent,  it  becomes  charged  with  various  electrolytes,  and 
its  freezing  point  is  consequently  lowered.  To  some  extent  this  immu- 
nizes the  mass  from  frost  action.  On  the  other  hand,  as  we  have  seen 
before,  cryohydric  compounds  may  be  formed  at  these  low  temperatures, 
and  the  separation  of  these  from  solution  is  a  factor  in  the  opposite 
direction. 

QUANTITY    OF   WATER   AT    FIRST   ADDED 

Size  of  cement  particles. — The  finest  particles  in  cement,  provided  that 
they  are  chemically  identical  with  the  remainder,  are  the  most  active 
oementitiously,  because  of  the  ease  of  reaction  and  of  the  greater  proba- 
bility of  this  action  being  uniform  throughout  the  mass  of  each  particle. 
This  is  recognized  under  the  microscope  by  the  ultimate  disappearance 
of  these  particles  as  individuals  upon  the  addition  of  water.  Owing  to 
the  relative  insolubility  of  the  constituents  of  cement,  both  before  and 
after  metamorphisni,  each  particle  becomes  covered  to  a  certain  depth 
with  the  reaction  products,  which  in  this  case  take  the  shape  of  gelatinous 
films  (2)  in  such  manner  as  to  offer  hindrance  to  the  further  action  of 
water. 

The  particles  whose  diameter  is  smaller  than  or  equal  to  the  thickness 
of  this  zone  evidently  are  the  most  efficient  chemically.  The  larger  par- 
ticles are  less  so.  as  the  passage  of  \vater  through  the  enveloping  film  is 
a  slow  matter,  and  some  particles  may  be  so  large  as  to  remain  internally 
unchanged.  It  is  probably  this  fact  that  gives  a  hydraulic  quality  to 
previously  set  cement  that  has  been  reground  and  retempered  with 
water;  in  fact,  this  process  may  be  repeated  a  number  of  times  with  the 
same  sample  of  cement. 

Xot  all  of  each  particle,  therefore,  can  take  part  in  the  setting  and 
hardening,  and  sometimes  this  proportion  of  inert  material  is  consider- 


METAMORPHISM    OF  PORTLAND   CEMENT  173 

able  (86).  The  coarser  particles  are  comparatively  inert  and  might  be 
replaced  by  grains  of  foreign  material  of  the  same  size  without  ma- 
terially influencing  the  ultimate  strength  of  the  resulting  mass.  This 
has  been  demonstrated  experimentally  (17).  It  does  not  follow,  how- 
ever, that  a  cement  consisting  entirely  of  uniformly  very  fine  particles 
would  be  a  desideratum,  since  such  a  cement  would  not  pack  as  well  as 
one  containing  a  greater  variety  of  sizes,  and  the  increase  in  chemical 
activity  would  be  markedly  overbalanced  by  the  imperfection  of  struc- 
ture of  the  mass.  Considering  each  particle  to  be  spherical,  and  of  equal 
size  with  every  other,  when  packed  in  the  most  compact  manner  possible 
the  pore  space  would  be  nearly  26  per  cent  (89).  The  points  of  contact 
of  the  adjacent  spheres,  notwithstanding  the  tendency  of  the  gelatinous 
envelope  to  spread,  would  be  relatively  few.  If,  however,  this  pore  space 
were  filled  with  finer  material,  the  structure  would  develop  more  strength. 
The  function  of  part  of  the  cement  is  to  remain  passive  and  to  add  to  the 
strength  of  the  structure  merely  by  its  action  of  void-filling.  Extremely 
fine  grinding  has  been  found  to  decrease  the  ultimate  strength,  if  the 
cement  is  used  neat,  but  to  give  greater  strength,  if  the  cement  is  used 
in  a  sand  mortar  (62). 

As  might  be  expected  from  the  above  considerations,  the  fineness  of 
grinding  has  an  accelerating  effect  upon  setting.  Cement  ground  in  a 
tube  mill  until  only  1  per  cent  remained  on  a  sieve  having  5000  meshes 
per  sq.  cm.,  was  so  quick  setting  that  it  could  not  be  restrained  even  by 
the  addition  of  10  per  cent  of  gypsum  (47).  When  cement  is  relatively 
coarsely  ground,  the  ultimate  strength  is  not  so  quickly  attained,  but  its 
acquisition  is  regular  and  uniform. 

Laitance. — In  concrete  construction  under  water,  especially  salt  water, 
there  gathers  about  the  freshly  deposited  concrete  a  milky  white  cloud  of 
suspended  matter,  technically  known  as  laitance.  This  material  is  also 
formed  when  concrete  is  mixed  very  wet,  though  not  deposited  under 
water. 

An  analysis  of  laitance  by  the  writer,  made  for  the  Board  of  Water 
Supply,  practically  coincides  with  an  analysis  made  by  Richardson  (97) 
and  leads  to  the  same  conclusion  as  that  reached  by  him;  namely,  that 
laitance  represents  an  actual  loss  of  cement  and  consists  of  the  finest  par- 
ticles of  cement  which  have  been  washed  out  of  the  concrete.  The  addi- 
tional conclusion  is  justified  that  this  portion  of  the  cement,  by  reason  of 
the  small  size  of  its  units,  has  been  so  acted  upon  by  an  excess  of  water 
that  it  has  undergone  complete  hydrolytic  decomposition,  before  the  col- 
loidal enveloping  film  had  adsorbed  sufficient  electrolytes  to  completely 
coagulate  it  and  so  render  it  largely  impermeable.  This  is  substantiated 
by  the  fact  that  laitance  possesses  neither  setting  nor  hardening  qualities. 


174  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

Hydrolysis  theory. — The  formation  of  such  a  protective  film  upon  the 
surface  of  a  coarse  particle  will  so  regulate  the  access  of  water  to  its 
interior  that  the  contents  will  be  slowly  and  normally  hydrated.  If  the 
entire  mass  of  the  particle  were  at  once  accessible  to  an  excess  of  water, 
the  weakly  acid  and  basic  compounds  at  first  formed  would  soon  be  hy- 
drolysed  and  shorn  of  their  binding  power,  and  instead  of  the  normal 
complex  colloids  described  by  Michaelis  (64,  65),  capable  of  adsorbing 
electrolytes  and  so  coagulating  into  a  dense  rigid  mass,  simpler  colloids 
such  as  hydrous  silicic  acid  and  aluminic  hydroxide  would  form,  which 
have  not  these  powers  to  so  high  a  degree. 

Finally,  the  rate  of  setting  and  hardening  of  a  cement  may  be  con- 
sidered a  function  of  the  proportion  of  fine  particles  present.  Mortars 
set  and  harden  more  slowly  than  neat  cement,  and  concretes  more  slowly 
than  either.  This  is  simply  a  development  of  the  fact  that  coarsely 
ground  cement  sets  and  hardens  more  slowly  than  that  which  is  finely 
ground.  It  may  be  considered.,  from  another  viewpoint,  that  the  inactive 
material  interferes  with  the  liberation  of  heat  from  the  system,  and  that 
chemical  reaction  is  consequently  delayed  in  proportion  to  the  amount 
of  inert  material  present. 

Mechanical  agitation  when  water  is  added. — If  cement  in  the  state  of 
a  plastic  mass  be  worked  and  kneaded,  the  ultimate  strength  will  benefit 
thereby,  up  to  a  maximum  time  of  working.  It  is  legitimate,  a  priori,  to 
surmise  that  the  setting  is  hastened,  within  limits,  although  no  record  of 
this  is  found. 

After  the  maximum  time  referred  to,  which  in  experiments  made  at 
the  Board  of  Water  Supply  laboratory  lias  been  found  to  correspond 
roughly  with  the  time  of  initial  set,  continued  working  will  cause  a  fall- 
ing off  in  the  strength.  Up  to  this  time,  mechanical  agitation  with  the 
proper  amount  of  gaging  water  will  cause  an  increase  in  the  ultimate 
strength. 

The  formation  of  the  crystalline  network,  which  constitutes  the  setting 
of  cement,  and  which  is  responsible  for  the  primary  strength  by  holding 
the  plastic  mass  rigid  and  in  place,  while  the  more  important  elements 
of  hardening  make  their  appearance,  is  unquestionably  facilitated  by 
agitation.  Stirring  is  a  means  of  hastening  chemical  reactions  by  bring- 
ing the  agents  into  more  intimate  contact.  The  compounds  that  go  to 
make  up  this  network,  being  sooner  brought  into  solution,  perform  their 
function  more  quickly,  and  the  crystals  begin  to  form.  Instead,  however, 
of  forming  a  continuous  rigid  network,  the  crystals  will  be  smaller  and 
less  cohesive  than  if  undisturbed  in  their  growth,  and  the  set  can  be 
delayed  and  even  prevented  by  continuing  the  agitation  long  enough. 


,   METAMORPHISM    OF   PORTLAND    C  EM  EXT  175 

The  ultimate  resistance  of  cement  which  has  been  thus  treated  is 
decreased  as  well.  The  formation  of  the  coagulated  colloid,  or  of  the 
interlocking  crystal  units,  whichever  may  be  the  cause  of  hardening,  is 
rendered  imperfect  and  discontinuous,  and  the  structure  reflects  the 
weakness  of  its  component  units. 

It  may  moreover  be  supposed  that  more  cement  has  been  brought 
within  the  range  of  hydrolysis  by  this  agitation,  and  so  converted  into 
laitance,  even  the  larger  particles  being  stripped  of  their  protecting  films 
by  the  attrition.  Tests  made  at  the  Watertown  Arsenal  (36)  showed  that 
after  one  hour's  working,  cement  had  gained  4  per  cent  over  the  normal 
strength,  but  that  after  10  hours'  working,  it  had  lost  24  per  cent  from 
the  normal,  in  20  hours  38  per  cent,  in  50  hours  56  per  cent  and  in  100 
hours  69  per  cent. 

Total  quantity  of  water  at  first  added. — Under  certain  conditions,  the 
entire  range  of  particles  of  a  cement  might  be  destructively  hydrolysed, 
resulting  in  what  is  termed  "drowned"  cement.  The  effect  of  an  increase 
in  the  quantity  of  mixing  water  is  known  to  result  in  a  diminution  of 
strength,  and,  bearing  in  mind  what  has  been  previously  said  regarding 
hydrolysis,  the  reason  is  clear.  If,  before  the  cementing  of  contiguous 
particles,  an  excessive  amount  of  water  is  admitted  to  contact  with  the 
cement,  colloidal  material  will  form  in  increased  amount.  It  has  been 
shown  that  an  increased  amount  of  mixing  water  results  in  an  increased 
volume  of  the  paste  produced  (39).  This  indicates  that  a  larger  amount 
of  the  products  of  hydrolysis  is  formed. 

Owing  to  difference  in  composition  between  these  hydrogels  and  those 
formed  under  normal  conditions,  they  are  incapable,  as  has  been  before 
observed,  of  adsorbing  electrolytes  in  such  degree  as  to  attain  to  the 
density  and  rigidity  of  the  latter.  Admitting,  on  the  other  hand,  that 
•colloids  so  formed  do  not  differ  in  composition  from  those  formed  in  the 
normal  hardening  of  cement,  there  still  remains  the  abnormality  of  the 
structure  formed  in  this  way.  Being  discontinuous,  it  would  not  offer 
the  same  total  resistance,  in  the  form  of  connected  films,  to  the  passage 
of  water.  Moreover,  in  the  presence  of  an  excess  of  water  the  working 
ratio  of  electrolytes  to  colloids  would  be  less  because  of  the  greater  dilu- 
tion in  proportion  to  the  volume  of  colloid. 

QUANTITY   OF  WATER   THAT  MAY   SUBSEQUENTLY   COME   INTO   CONTACT 

WITH    THE    SYSTEM 

+ 

The  effect  of  water  upon  cement  after  it  has  completely  set  rapidly 
diminishes  to  a  negligible  quantity  at  ordinary  temperatures,  if  the  water 
is  reasonably  free  from  dissolved  or  suspended  impurities.  There  is  a 


176  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

leaching  out  of  calcium  hydroxide  from  the  mass  of  the  cement ;  but  this 
diminishes  as  the  mass  grows  more  and  more  impermeable,  by  the  coagu- 
lation of  the  colloidal  cell  walls  and  by  the  carbonation  or  other  precipi- 
tation of  lime  salts  in  the  pores. 

This  deposition  of  lime  salts  in  the  pores  is  evidently  the  cause  of 
higher  strength  in  specimens  which  are  allowed  to  dry  out  a  few  hours 
before  testing.  It  is  analogous  to  the  higher  strength  developed  by  sea- 
soned stone  than  by  freshly  quarried  stone,  occasioned  by  the  evaporation 
of  the  "quarry  sap."  In  addition,  the  carbon  dioxide  conveyed  to  the 
material  in  a  gaseous  form  is  absorbed  by  the  lime  and  may  be  considered 
a  positive  factor  towards  strength,  while  that  conveyed  in  solution  (where 
the  cement  is  under  water)  is  a  negative  factor,  in  that  it  accelerates  the 
solvent  effect  of  the  water  coming  into  contact  with  the  cement.  On  the 
other  hand,  cement  specimens  which  are  entirely  air-hardened  are  un- 
questionably weaker,  by  reason  of  the  absence  through  evaporation  of  the 
requisite  amount  of  water  for  proper  hydration. 

When  the  action  of  water  upon  set  cement  is  intermittent,  the  solvent 
effect  manifests  itself  by  unsightly  incrustations  and  discolorations  (3), 
caused  by  dissolved  material  brought  to  the  surface  through  capillary 
action  and  there  deposited  by  evaporation.  When  the  mass  is  perma- 
nently under  water,  these  salts  are  merely  washed  away.  The  danger 
from  these  incrustations,  although  slight,  is  the  disintegrating  effect  pro- 
duced by  their  increase  in  volume,  through  crystallization  or  efflorescence, 
and  the  consequent  disruption  of  the  denser  surface  skin,  rendering 
easier  the  action  of  frost  upon  the  entire  mass. 

This  surface  skin  is  improved  by  troweling  the  cement  while  in  a 
plastic  state,  and  consists  of  a  closely  packed  layer  of  fine  particles,  which 
offers  high  resistance  to  permeation  by  water  and  comparative  immunity 
from  the  solvent  action  favored  by  a  rough,  porous  or  fractured  surface. 

If  the  mass  be  placed  in  water  before  setting,  it  is  more  liable  to  hy- 
drolysis, as  evidenced  by  the  copious  formation  of  laitance;  and  if  greatly 
exposed,  as  by  agitation  under  \vater,  it  may  fail  to  develop  the  greater 
portion  of  its  normal  ultimate  strength.  To  prevent  this,  care  is  taken, 
in  laying  concrete  under  water,  so  to  convey  it  that  it  offers  the  least 
possible  surface  to  water  action  during  its  descent;  and  to  this  end  it  is 
either  lowered  in  cloth  bags,  or  filled  in  through  a  chute,  so  as  to  escape 
all  avoidable  exposure  to  hydrolysis. 

If  the  water  which  comes  in  contact  with  a  cement  structure  be  under 
considerable  pressure,  so  that  its  tendency  is  to  percolate  through  the 
mass,  the  solvent  effects  will  of  course  be  magnified,  proportionally  to  the 
porosity  of  the  mix ;  and  experiments  made  by  the  Board  of  Water  Supply 


PACIXI,   METAMORPHI8M    OF  PORTLAND   CEMENT  177 

have  shown  that  concrete  subjected  to  such  percolation  has  been  shorn  of 
the  major  portion  of  its  ultimate  strength.  In  this  case,  the  solvent 
effect  of  the  water  is  only  part  of  the  influence  at  work,  purely  me- 
chanical factors  entering  largely  into  the  destructive  process,  as  will  be 
shown  late$. 

Stalactitic  growths  of  lime  salts  form  as  the  result  of  water  percolating 
through  concrete.  Micro-organisms  of  the  algal  type  frequently  lodge  in 
the  pores  of  concrete  and  by  their  growth  may  act  as  a  protective  influ- 
ence against  the  permeation  of  water.  The  effect  of  their  products  of 
metabolism  and  decay  upon  the  concrete  structure  has  not  been  studied. 

Numerous  waterproofing  materials  and  processes  have  been  devised 
(40,  73).  They  may  be  grouped  conveniently  under  three  heads. 

Surface  treatments. — The  application  to  the  surface  of  concrete  of  a 
coating  similar  to  a  paint  has  the  disadvantage  that  concrete  is  not  a 
thoroughly  dry  material.  Where  the  vehicle  is  a  liquid  immiscible  with 
water,  the  paint  will  not  therefore  come  into  contact  with  the  concrete 
proper.  If  the  vehicle  is  miscible  with  water,  unless  insoluble  products 
are  at  once  formed  by  reaction  with  the  constituents  of  cement,  the 
active  agent  is  quickly  leached  out. 

Membranes. — These  are  layers  of  waterproof  tissue  interposed  between 
two  layers  of  the  concrete.  There  is  strong  probability  that  these  never 
actually  form  a  bond  with  the  concrete,  and  thus  they  necessarily  intro- 
duce an  element  of  weakness  and  heterogeneity. 

Mass  treatments. — The  active  material  is  incorporated  with  the  con- 
crete at  the  time  of  mixing,  either  by  dissolving  or  suspending  in  the 
gaging  water,  or  by  intimately  mixing  with  the  cement  or  sand.  These 
treatments  are  many  and  differ  widely  in  the  agents  employed.  Sub- 
stances of  a  waxy  or  fatty  nature,  triturated  to  a  great  fineness,  are  the 
most  generally  offered,  but  the  incorporation  of  these  in  a  mass  of  con- 
crete is  generally  followed  by  weakness  of  the  structure.  The  general 
problem  of  cement  waterproofing  has  been  conceded  to  be  simply  a  ques- 
tion of  void-filling,  yet  this  must  be  accomplished  without  the  addition 
of  inert  material  that  will  weaken  the  resulting  structure. 

The  addition  of  more  colloidal  material  has  been  suggested.  This  is 
ingeniously  effected  in  a  recent  process  by  the  use  of  hydrolysed  cement, 
obtained  by  treating  cement  with  an  excess  of  water  (99).  The  paste  so 
obtained  is  added  to  the  cement  during  mixing. 

The  still  unclarified  state  of  our  knowledge  of  the  chemistry  of  the 
setting  andjiardening  of  cement  is  the  great  handicap  which  has  thus  far 
prevented  the  devising  of  a  satisfactory  waterproofing  agent.  A  large 
number  of  the  waterproofing  preparations  on  the  market  are  therefore 


178  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

purely  empirical,  and  not  applicable  to  the  practical  waterproofing  of 
large  masses  of  constantly  wet  concrete.  In  the  interests  of  efficiency,  it 
is  probably  more  economical  to  expend  money  destined  for  waterproof- 
ing in  the  purchase  of  additional  cement  to  be  used  in  making  a  richer 
concrete. 

QUALITY  OF  WATER  AT   FIRST   ADDED 

Having  material  in  solution. — On  adding  water  to  cement,  heat  is 
evolved,  the  temperature  of  the  mix  rising  in  some  cases  to  above  the 
boiling  point  of  water.  It  is  the  custom  to  look  with  suspicion  upon 
i-ements  in  which  an  excessive  rise  of  temperature  is  obtained,  as  being 
liable  to  develop  unsoundness.  The  abnormal  rise  is  attributed  in  some 
instances  to  the  presence  of  free  lime,  in  others  to  an  insufficient  propor- 
tion of  lime.  The  volume  changes  caused  by  a  rise  in  temperature  have 
been  given  as  the  reason  of  the  difficulty  encountered  in  joining  fresh 
•cement  surfaces  to  old,  causing  weakness  at  the  plane  of  juncture,  the 
contraction  o«f  the  mass  on  cooling  breaking  the  joint  before  it  has  devel- 
oped sufficient  strength  to  resist  the  strain. 

To  prevent  this,  it  has  been  suggested  to  coat  the  surface  to  which 
fresh  cement  is  to  be  applied  with  a  retempered  mortar :  that  is,  with  a 
cement  which  has  been  treated  with  water  after  partial  setting.  This 
provides  an  intermediate  course  of  material  in  which  the  temperature 
changes  are  not  so  rapid,  and  upon  this  course  the  fresh  cement  mixture 
is  applied  (35). 

Upon  the  same  principle  may  be  explained  the  use.  for  a  fresh  course 
of  cement  which  is  to  be.  joined  to  some  which  has  previously  set,  of 
mixing  water  in  which  a  quantity  of  cement  has  been  stirred,  thus  retard- 
ing the  chemical  reaction  and  consequent  temperature  changes.  In  both 
cases,  the  active  water  is  already  charged  with  the  soluble  portion  of 
cement,  its  solvent  power  for  the  same  material  is  thereby  diminished 
and  the  chemical  action  moderated,  so  that  heat  is  more  gradually 
evolved  and  violent  expansions  and  contractions  avoided. 

The  influence  of  dissolved  electrolytes  in  mixing  water  has  received 
much  careful  study.  Through  the  addition  of  a  small  percentage  of 
some  soluble  salt  to  the  mixing  water,  many  have  tried  to  influence  the 
properties  of  the  completed  structure  and  to  produce  a  mass  that  would 
develop  greater  strength  or  a  higher  degree  of  imperviousness.  Unfor- 
tunately, the  panacea  has  not  as  yet  been  discovered  that  is  suitable  for 
practical  application. 

The  addition,  similarly,  of  a  soluble  powder  incorporated  in  the  mass 
of  the  cement  comes  under  the  same  category.  In  this  connection,  our 


P  ACINI,   METAMORPHISM   OF  PORTLAND   CEMENT  179 

attention  is  drawn  to  the  effect  of  the  usual  addition  of  ground  gypsum 
or  of  plaster  of  Paris  to  the  ground  clinker,  for  the  purpose  of  retarding 
the  set.  There  are  other  salts  whose  retarding  influence  on  the  set  of 
ground  clinker  is  comparable  and  probably  superior  to  that  of  gypsum, 
but  their  use  is  not  so  practical,  consequently,  it  has  been  adopted  as  the 
restrainer  for  general  use. 

It  has  been  shown  by  Kohland  (83)  that  the  salts  which  respectively 
accelerate  and  retard  the  setting  of  cement  are  the  same  as  those  which 
accelerate  and  retard  the  hydration  of  quicklime.  From  this  it  is  con- 
cluded that  their  influence  is  "catalytic." 

A  detailed  explanation  of  the  mechanism  of  the  action  of  gypsum  has 
been  put  forth  (79),  holding  that  the  presence  of  calcium  ions  in  the 
mixing  water,  resulting  from  the  solution  of  gypsum  therein,  decreases 
the  solution  of  other  calcium  ions,  thus  retarding  the  solution  of  lime 
and  the  hydrolysis  of  the  aluminates,  which  in  turn  retards  the  set. 

It  seems  probable,  upon  this  basis,  that  the  presence  of  certain  elec- 
trolytes in  the  mixing  water  acts  upon  the  set  by  influencing  the  solu- 
bility of  calcium  sulphate  therein,  and  consequently  increasing  or  dimin- 
ishing the  number  of  calcium  ions  present  in  the  mixing  water  as  a  result 
of  the  solution  of  calcium  sulphate. 

For  example,  sea  water  has  been  found  to  retard  the  set  of  cement 
(83).  Gypsum,  although  a  relatively  insoluble  salt,  may  be  regarded  as 
fairly  soluble  in  moderately  strong  solutions  of  sodium  chloride  or  of 
other  salts  having  no  common  ion  (14).  In  the  presence  of  sodium 
chloride,  then,  the  calcium  ion  concentration  in  the  mixing  water  is 
raised,  and  the  solution  of  the  calcium  aluminates  diminished,  with  the 
effect  of  retarding  the  set.  Sulphates  have  been  found,  when  dissolved 
in  the  mixing  water,  to  have  the  property  of  retarding  the  set,  with  the 
exception  of  aluminum  sulphate  and  calcium  sulphate  when  in  low  con- 
centration. In  view  of  the  latter  fact,  it  is  evident  that  the  above  expla- 
nation is  perhaps  only  a  partial  one. 

A  large  number  of  other  electrolytes  and  miscellaneous  compounds 
have  been  investigated  and  the  results  are  recorded  (83). 

The  effect  of  soluble  constituents  in  the  sand  used  for  making  concrete 
is  by  no  means  negligible  (4)  and  may  offer  an  explanation  for  many 
instances  of  puzzling  behavior  of  the  mixture. 

Sea  water  has  been  and  is,  in  many  instances,  still  used  for  mixing  con- 
crete, and  to  the  best  of  our  knowledge,  no  cases  of  failure  can  be  attrib- 
uted to  this  cause  alone.  Apart  from  the  influence  upon  setting,  the 
presence  of  dissolved  electrolytes  in  the  mixing  water  seems  to  increase 
the  strength  of  cement  in  the  early  periods,  as  fa-r  as  reported  results  have 


1§0  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

shown  (4).  This  may  perhaps  be  due  to  an  increase  of  coagulation  of 
the  colloidal  constituents,  by  reason  of  the  presence  of  salts  of  greater 
ionization  than  are  generally  present.  On  the  basis  of  the  crystallization 
theory,  this  phenomenon  is  rather  difficult  to  interpret. 

QUALITY   OF   WATER   THAT   MAY   SUBSEQUENTLY    COME   IXTO   CONTACT 
WITH    THE    SYSTEM 

Having  material  in  solution. — A  large  number  of  failures  in  concrete 
structures  have  been  attributed  to  the  disintegrating  action  thereon  of 
water  impregnated  with  various  salts.  Inasmuch  as  all  ground  water  is 
charged  to  some  degree  with  salts  which  it  has  accumulated  in  its  passage 
through  the  soil  and  rocks,  this  problem  is  worthy  of  the  most  careful 
attention.  For  our  purpose,  such  mineral-laden  waters  may  be  divided 
into 

1.  Sea  water 

2.  Alkali  water  (from  western  alkali  soils) 

3.  Deep  rock  waters. 

The  mineral  constituents  are  common  in  all  these  cases,  and  vary  only 
in  the  prominence  of  one  or  more  of  them.  Thus  in  sea  water  the  chlo- 
rides of  sodium  and  magnesium,  in  alkali  water  the  alkaline  carbonates, 
and  in  deep  rock  water  the  chlorides  of  calcium  and  magnesium  and  the 
sulphate  of  magnesium  are  the  distinctive  constituents.  Whether  the 
effect  of  these  electrolytes  is  cumulative,  so  that  the  continued  action  of 
solutions  of  low  concentrations  will  work  harm,  or  if  not,  what  are  the 
limiting  concentrations  to  assure  safety  to  the  structure,  has  not  been 
worked  out.  Obviously,  it  is  not  a  laboratory  problem,  since  the  factors 
which  obtain  in  nature  are  impossible  to  duplicate  on  a  small  scale.  The 
solution  lies  in  careful  inquiry  into  the  mechanism  of  the  action  and  in 
observation  of  the  instances  of  failure  in  construction  work,  with  a  study 
of  its  causes. 

Sea  water. — The  effects  of  sea  water  upon  set  cement  have  been  sum- 
marized in  the  statement  by  Feret,  "Xo  cement  has  yet  been  found  which 
presents  absolute  security  against  the  decomposing  action  of  sea  water" 
(97).  Le  Chatelier,  after  a  series  of  experiments  extending  over  ten 
years,  confirms  this  conclusion  (53).  Poulsen  concludes,  however,  that 
the  chemical  action  of  salt  water  is  not  alone  sufficient  to  cause  Portland 
cement  mortars  to  deteriorate  (76). 

The  diversity  of  results  reported  in  the  observation  of  the  action  of 
sea  water  upon  cement  indicates  that  there  are  varying  factors  at  work 
that  so  far  have  not  been  clearly  recognized.  Whether  the  precise  nature 


PACINI,   METAMORPHIS1I    OF  PORTLAND    CEMENT  1§1 

of  the  action  is  physical  or  chemical  is  not  quite  settled.  There  are  not 
lacking  investigators  who  assert  that  the  destructive  action  is  mostly 
physical  and  is  due,  among  other  causes,  to  intermittent  submergence 
and  consequent  deposition,  by  evaporation  of  crystals  in  the  pores  of  the 
structure,  -"which,  either  by  their  pressure  of  formation  or  by  expansion 
during  efflorescence,  have  a  disruptive  effect  similar  to  that  of  frost  (98). 

There  are  those  who  hold  that  the  action  is  entirely  physical,  and  is 
due  to  this  factor  and  the  effects  of  frost  (91,  102),  although  probably 
the  latter  is  seldom  the  case  in  sea  water,  owing  to  its  low  freezing  point 
(50).  The  effect  of  direct  sunshine  has  been  found  deleterious  when 
alternating  with  that  of  tidal  action  (20).  Undoubtedly,  all  of  these 
factors  contribute  to  the  total  effect,  and  there  is  as  well  a  marked 
chemical  action. 

The  chemical  effects  of  sea  water  upon  cement  are  capable  of  various 
interpretations.  They  are  summarized  as  the  formation  of  complexes  by 
the  action  of  the  dissolved  sulphates  and  chlorides  in  the  water  upon  the 
calcium  silicates  and  alummates  of  the  cement  (74).  It  has  been  stated 
that  sodium  chloride  solutions  have  the  power  of  dissolving  calcium  sili- 
cate with  the  formation  of  an  unknown  salt  (58,  70),  and  also  that  the 
sodium  chloride  enters  into  combination  in  the  mass,  the  chlorine  ion 
entering  into  the  combination  calcium  chloro-aluminate,  and  the  sodium- 
ion  combining  with  lime,  silica  and  alumina,  to  form  compounds  of  the 
nature  of  the  zeolites. 

Working  with  strong  solutions  of  the  individual  salts  of  sea  water,  it 
has  been  found  that  the  chief  harmful  constituent  is  magnesium  sulphate, 
and  it  has  been  suggested  that  this  salt  reacts  with  the  lime  of  the  cement 
to  form  calcium  sulphate  and  magnesium  hydroxide.  The  calcium  sul- 
phate further  reacts  with  calcium  aluminate  to  form  a  calcium  sulpho- 
aluminate,  which  by  swelling  causes  the  disruption  of  the  mass.  The 
magnesium  hydroxide  formed  has  been  regarded  as  a  restraining  agent, 
by  virtue  of  its  filling  up  the  pores  of  the  cement  and  preventing  further 
ingress  of  sea  water  (70).  Again,  the  disruption  has  been  directly  at- 
tributed to  the  increase  of  volume  caused  by  the  formation  of  this  mag- 
nesium hydroxide  (46).  It  has  been  calculated  that,  apart  from  the 
formation  of  hypothetical  sulpho-aluminates,  a  molecularly  equivalent 
amount  of  calcium  sulphate  replacing  the  calcium  hydroxide  of  the  ce- 
ment occupies  2.08  times  as  much  space  and  is,  therefore,  the  cause  of 
the  disintegration  (13). 

Alkali  and  deep  rock  waters. — Burke  and  Pinckney  (13)  have  formu- 
lated a  wofking  theory  of  the  action  of  the  various  salts  common  to  all 
natural  waters.  They  attribute  the  disruptive  action  to  more  rapid  re- 


182  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

moval  of  the  calcium  hydroxide,  and  in  some  cases  to  its  replacement  by 
material  occupying  greater  volume,  as  before  shown,  and  consequent 
disintegration  of  the  structure. 

That  some  such  reactions  occur  is  indubitable,  and  that  the  mechanical 
factors  are  a  large  influence  in  the  disintegration  is  equally  certain.  An 
additional  cause  which  may  be  of  great  importance  has  hitherto  been 
neglected.  The  electrolytes  in  these  natural  waters  may  act  as  acceler- 
ators of  hydrolysis,  and,  in  effect,  cement  which  is  in  contact  with  sea 
water  is  subject  to  the  same  action  as  that  of  an  excess  of  water  from  any 
cause.  By  the  presence  of  these  electrolytes  the  hydrolysis  of  a  larger 
proportion  of  the  cement  is  effected;  and  the  results  are  increase  in  tlia 
volume  of  the  hydrolysed  portion,  and  production  of  a  larger  proportion 
of  inert  colloids.  It  has  been  found  that  a  larger  amount  of  cement  can 
be  converted  into  colloidal  matter  by  the  presence  of  an  electrolyte  in 
the  water  with  which  it  is  treated  (99),  and  also  that  the  speed  of  hydra- 
tion  of  cement  is  affected  by  the  presence  and  proportion  of  electrolytes 
present  (84).  The  fact  that  a  larger  amount  of  laitance  appears  to  be 
formed  in  sea-water  construction  also  seems  to  bear  out  this  theory. 

Besides  the  reactions  mentioned,  set  cement  is  subject  to  the  replace- 
ment of  silicic  acid  by  carbonic  acid,  as  are  the  natural  rocks.  Especially 
is  this  true  in  cases  where  the  cement  comes  into  contact  with  marsh  and 
peaty  waters  and  waters  containing  ferrous  carbonate,  which  by  transfor- 
mation to  the  hydroxide  liberates  carbon  dioxide  (24),  which  has  been 
found  to  act,  not  only  upon  the  calcium  hydroxide  but  also  upon  the 
silicates  and  aluminates  (28). 

The  presence  of  free  acids  in  water  which  acts  upon  the  cement  is 
quite  destructive,  in  proportion  to  the  concentration  of  the  acid  and  to 
its  strength  or  weakness  as  an  acid.  It  is  quite  probable,  however,  that 
the  liberation  of  colloidal  silica  by  the  action  of  acids  would  serve  to  a 
great  extent  as  a  protective  influence  against  their  further  action. 

Sewage  gases  are  generally  effective  by  reason  of  the  hydrogen  sulphide 
which  they  contain.  This  gas  is  readily  oxidized  to  sulphuric  acid,  and 
then  its  action  is  the  production  of  soluble  calcium  and  aluminum  sul- 
phates, which  are  subsequently  leached  out  from  the  mass.  This  action 
has  been  found  greatest  at  the  surface  of  the  liquid  (106).  Hydrogen 
sulphide  may  also  act  by  converting  the  iron  of  the  cement  into  sulphide, 
and  this  becomes  oxidized  into  ferrous  sulphate  and  is  leached  out,  or  by 
its  expansion  causes  disruption  (28). 

The  action  of  many  other  inorganic  and  organic  solutions  has  been 
observed,  but  they  do  not  come  within  the  scope  of  this  paper,  since  they 
are  not  met  with  in  natural  processes. 


PACIXI,   METAMORPHISM   OF  PORTLAND   CEMENT  133 

In  general,  the  consideration  is  worthy  of  attention  whether  concrete 
structures  which  are  under  stress  are  not  more  liable  to  chemical  disin- 
tegration than  those  which  are  in  repose,  or  whether  a  single  structure  is 
not  more  liable  to  this  action  in  its  strained  parts  than  in  those  not  so 
affected.  We  have  data  to  show  that  strained  iron  is  more  liable  to  corro- 
sion than  unstrained,  and  it  has  been  asserted  that  strained  minerals  are 
more  acted  upon  by  underground  solutions  (104). 

A  number  of  protective  measures  against  the  action  of  saline  waters 
upon  concrete  have  been  suggested  and  tried,  but  none  has  been  so  strik- 
ingly effective  as  to  achieve  universal  recognition.  The  simplest  remedy 
suggested  is  to  make  the  concrete  for  such  uses  denser  and  more  imper- 
vious by  the  employment  of  a  greater  proportion  of  cement,  yet  this  may 
not  always  be  practicable.  When  concrete  is  exposed  to  the  gases  result- 
ing from  the  decomposition  of  sewage,  it  is  suggested  that  even  such  a 
proceeding  may  be  of  no  avail  (29). 

Previous  air-hardening  of  the  concrete  before  laying  under  sea  water 
is  acquiring  more  widespread  use  and  is  highly  recommended  (87). 
The  cause  of  its  protective  action  is  attributed  to  the  carbonation  of  the 
calcium  hydroxide  (48). 

Variations  in  the  fineness  of  grinding  and  in  the  chemical  composition 
of  the  cement  used  in  concrete  for  sea-water  construction  have  been  pro- 
posed. The  French  specifications  for  sea-water  cements  call  for  a  finer 
grinding  than  that  which  is  required  for  ordinary  construction.  Much 
has  been  claimed  regarding  the  resistance  to  disintegration  offered  by  the 
so-called  "iron  ore"  cement,  which  contains  a  minimum  of  alumina,  this 
being  almost  entirely  replaced  by  iron. 

Having  material  in  suspension. — The  peculiar  nature  of  the  series  of 
compounds  forming  and  formed  from  cement,  in  that  they  are  all  of 
relatively  low  solubility,  tends,  as  has  been  before  observed,  to  retard  the 
reactions  which  may  occur.  Mechanical  agitation,  by  promoting  diffu- 
sion and  by  transporting  the  reacting  materials  to  their  possible  spheres 
of  action,  will  accelerate  these  reactions.  The  motion  of  water,  per  se, 
can  and  does  produce  this  effect,  and  when  the  water  is  armed  with  sus- 
pended material,  its  activity  in  this  direction  is  greatly  enhanced. 

Where  water  has  immediate  access  only  to  the  outer  surface  of  a  mass 
of  set  cement  and  its  pressure  is  low,  the  effect  is  a  slow  corrasion  of  the 
dense  surface  skin  and  ultimate  removal  thereof,  rendering  the  interior 
gradually  more  accessible.  Ordinarily,  this  process  is  a  slow  one,  al- 
though under  certain  conditions,  as  in  coast  protection  works  where  the 
velocity  of  the  water  is  high  and  the  suspended  material  coarse  and 
plentiful,  the  destructive  effects  are  more  to  be  reckoned  with. 


184  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

The  effects  from  less  spectacular  processes  are  quite  surprising.  Where 
the  pressure  of  the  water  is  such  that  there  is  a  marked  motion  of  the 
water  within  the  pores  of  the  concrete,  the  erosion  is  internal  and  far 
more  insidious.  In  this  case,  the  suspended  material  is  part  of  the  struc- 
ture itself.  Small  particles  of  cement  or,  in  the  case  of  mortar,  grains 
of  sand  which  become  detached  from  the  parent  mass  are  whirled  around 
by  the  water  stream  and  shortly  enlarge  the  cavity  in  which  they  are 
rotating,  until  it  merges  with  some  adjacent  cavity.  Under  favorable 
conditions  this  process  may  continue  until  the  interior  of  the  structure 
is  greatly  weakened. 

A  factor  which  to  some  extent  neutralizes  the  flow  of  water  through 
concrete  is  the  choking  of  the  pores  by  sediment,  coming  from  the  water 
itself  or  furnished  by  the  action  of  the  water  upon  the  concrete.  If  the 
flow  is  oscillatory,  as  in  concrete  exposed  to  the  range  of  the  tides,  this 
protective  effect  will  of  course  not  be  so  marked  (54). 

Diatoms  and  other  microscopic  marine  organisms  with  siliceous  or  cal- 
careous tests  undoubtedly  play  an  extensive  part  in  the  preliminary- 
stages  of  this  internal  mechanical  action,  by  choking  the  capillary  spaces. 
At  the  same  time,  undoubtedly,  the  organic  debris  thus  introduced  may 
by  its  decomposition  give  rise  to  substances,  carbon  dioxide  and  hydrogen 
sulphide,  for  example,  which  have  an  accelerating  action  upon  the  proc- 
esses of  solution,  and  the  silting  effect  may  thus  be  neutralized  or  even 
overbalanced. 


PART  II 
EXPERIMENTAL  INVESTIGATION' 

In  Part  I,  the  ways  in  which  water  may  influence  the  metamorphism 
of  Portland  cement  were  discussed  qualitatively,  and  their  possible  effects 
upon  the  permanence  of  the  structure  of  which  cement  forms  the  basis 
were  pointed  out.  This  question  has  now  assumed  economic  and  vital 
importance. 

In  the  following  pages  experimental  data  are  offered,  in  elaboration  of 
the  outline  laid  down  in  the  first  portion  of  the  paper.  Points  in  the 
scheme  which  have  been  established  beyond  doubt  by  previous  investi- 
gators are  here  omitted,  and  only  such  results  are  inserted  as  have  been 
deemed  necessary  as  additional  evidence.  The  last  division  of  the  out- 
line, treating  of  the  action  of  suspended  material  in  water  in  effecting 
the  erosion  of  concrete,  has  not  been  experimented  upon,  not  having  come 
within  the  scope  of  the  writer's  activities,  and  therefore  is  omitted. 


PACINI,   METAMORPHISM    OF   PORTLAND    CEMEST  185 

Other  divisions  have  already  been  so  thoroughly  covered  by  previous  in- 
vestigators that  very  little  remains  to  be  said  about  them.  Emphasis  has 
therefore  been  laid  in  this  paper  upon  the  little  known  fields. 

The  problems  which  confront  the  user  of  concrete  are  of  a  high  order 
of  complexity..  The  generalizations  of  chemistry  are  not  yet  sufficiently 
developed  to  apply  rigidly  to  systems  of  so  many  variables,  and  experi- 
mental work  on  a  laboratory  scale  often  fails  almost  entirely  to  reproduce 
the  conditions  of  practice.  The  best  guide  to  the  truth,  then,  is  the  prag- 
matic sanction  of  experience — the  investigator  in  this  field  can  but  point 
out  probable  directions  for  future  experimentation.  The  theories  which 
underlie  past  success  are  a  safe  guide,  nevertheless,  to  future  construc- 
tion, and  the  systematization  thereof  is  a  legitimate  field  of  usefulness. 

While,  strictly  speaking,  any  aggregation  of  chemical  compounds 
might  be  considered  a  rock,  whether  natural  or  artificial,  a  majority  of 
the  cases  conceivable  under  such  a  classification  would  not  present  im- 
portant petrological  problems  in  the  study  of  their  metamorphism.  Such 
a  problem  as  the  action  of  water  upon  a  mixture  of  sodium  chloride  and 
calcium  sulphate  can  be  partly  solved  in  vitro,  even  though  the  action 
of  sea  water  upon  gypsum  deposits  is  an  interesting  petrological  investi- 
gation. 

The  important  components  of  Portland  cement  are  everywhere  about 
us  in  nature,  and  the  reactions  by  which  it  is  made  artificially  have  been 
taking  place  for  many  geological  ages  without  the  intervention  of  man. 
Silica,  alumina  and  lime  are  among  the  most  important  constituents  of 
the  earth's  crust;  they  are  subjected  in  places  to  the  same  conditions 
that  exist  in  the  kiln,  and  are  afterwards  acted  upon  by  water,  under 
some  of  the  same  conditions  under  which  man  builds  massive  structures. 

The  complex  question  of  the  history  of  rock  magmas  is  not  one  to  be 
solved  by  any  one  group  of  scientists,  but  by  patient  and  concerted  efforts 
of  the  chemist,  the  physicist  and,  above  all,  the  petrologist.  So  the  prob- 
lem of  the  constitution  of  Portland  cement  may  be  as  yet  somewhat  inde- 
terminate ;  but  an  examination  of  the  more  general  effects  of  metamor- 
phism may  reveal  some  identity  with  conditions  in  natural  rocks  already 
studied  and  may  direct  us  to  the  correct  methods  for  investigation  of  the 
constitution  of  cement  (67). 

Other  important  problems  in  the  field  of  cement  and  concrete  are  re- 
ferred to  in  the  following  pages,  and  belong  in  great  measure  to  the  field 
of  petrology.  Not  the  least  important  of  these  is  the  suitability  of  vari- 
ous types  of  rocks  for  use  as  aggregates  in  concrete,  and  this  work  is 
claiming  more  widespread  attention  daily  (19,  44,  111). 


186 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


TEMPERATURE   OF   THE   WATER  AT   FIRST  ADDED 

Two  standard  cements  were  gaged  with  the  requisite  quantity  of  mix- 
ing Avater  for  each  at  different  temperatures.  The  effect  upon  the  time 
of  initial  and  final  set  was  noted,  as  follows : 

TABLE  1 
Effect  of  Temperature  of  Gaging  Water  on  Time  of  Initial  and  Final  Set 


Per  cent  by  weight 
of  mixing  water 

Temperature  of 
mixing  water 

Initial  set, 
hours 

Final  set. 
hours 

A 

B 

A  and  B 

A 

B 

A               B 

22 

21 

70°  F. 

4.25 

4.50 

6  .  75           7  .  50 

22 

2J 

100°  F. 

1.50 

4.00 

4.00           7.00 

•» 

21 

150°  F. 

0.33 

3.75 

0.50           5.75 

22 

21 

212°  F. 

1.00 

2.75 

2.75           6.00 

The  results  seem  to  indicate  that  interference  of  hydrolytic  decompo- 
sition with  the  setting  appears  between  150°  F.  and  the  boiling  point  of 
water.  Below  these  limits,  the  effect  of  increase  of  temperature  of  the 
mixing  water,  as  is  well  known,  is  to  increase  the  speed  of  setting  (31). 
The  setting  time  at  these  temperatures  is  a  resultant  of  two  opposed 
processes, — the  formation  of  the  water  crystalline  network,  and  the  de- 
structive hydrolytic  action  of  water  upon  the  original  constituents  of  the 
cement,  resulting  in  a  product  which  has  no  hydraulic  qualities. 

Where  the  second  process  overbalances  the  first  is  the  point  at  which 
the  speed  of  setting  ceases  to  increase  and  begins  to  diminish. 

This  is  true  of  course  of  the  stage  known  technically  as  the  final  set 
(9).  In  the  first  few  hours  of  setting,  there  is  a  period  of  relaxation, 
which  McKenna  has  aptly  termed  reverse  set,  and  which  he  has  been 
able  to  detect  with  precision  by  means  of  an  ingenious  chronographic 
apparatus  of  his  invention  (60).  The  phenomenon  has  been  observed  by 
the  writer  and  his  associates  in  the  laboratory  of  the  Board  of  Water  Sup- 
ply, using  the  Vicat  needle;  but  this  apparatus  does  not  lend  itself  to  a 
scientific  study  of  the  finer  differences  in  rigidity  which  occur  during  the 
setting  period.  Mclvenna's  apparatus  should  throw  a  great  deal  of  light 
upon  the  initial  metamorphism  of  cement. 


TEMPERATURE  OF  THE  WATER  THAT   MAY   SUBSEQUENTLY    COME   IXTO 
CONTACT    WITH    THE    SYSTEM 

High  pressure  steam. — Wig  (109)  has  recently  presented  an  account 
of  the  excellent  effects  of  high  pressure  steam  when  used  in  curing  con- 


PACIXI,   METAMORPHISM   OF  PORTLAND   CEMENT 

crete.  He  found  that  by  using  concrete  that  had  attained  its  initial  set 
and  exposing  it  to  steam  at  80  pounds  pressure  the  six  months'  strength 
could  be  obtained  in  two  days,  a  tremendous  accelerating  of  the  harden- 
ing process. 

This  state  of  affairs  is  not  very  satisfactorily  explained,  if  the  harden- 
ing of  cement  is  supposed  to  be  due  to  the  progressive  crystallization  of 
calcium  hydroxide,  since  it  is  somewhat  at  variance  with  our  knowledge 
of  the  conditions  of  crystallization  to  assert  that  continuous  exposure  to 
a  high  temperature,  presumably  constant,  should  accelerate  crystalliza- 
tion; particularly  since  in  this  case  the  amount  of  water  present  in  the 
system  remains  the  same.  On  the  basis  of  the  colloid  theory,  however,  it 
is  simply  explained  by  supposing  that  adsorption  of  calcium  hydroxide 
by  the  complex  hydrogel  is  accelerated  by  higher  temperatures. 

Cold  storage. — A  series  of  tests,  embracing  neat  cements  and  mortars, 
was  made  upon  tensile  test  specimens  exposed,  after  the  age  of  24  hours, 
to  low  temperatures  under  diverse  conditions.  The  following  conditions 
were  observed : 

1.  Chilling  the  briquettes  at  24  hours'  age  by  filling  the  storage  tank 
with  water  at  the  lowest  winter  temperature  as  it  came  from  the  tap. 
The  water  was  then  allowed  to  come  slowly  to  normal  winter  temperature 
for  the  tank,  about  60°  F. 

2.  Chilling  another  set  of  specimens,  otherwise  normally  treated,  In- 
filling the  tank  with  cold  water  as  before,  24  hours  before  breaking. 

3.  Storing  another  set  in  ice  water  for  the  entire  period  after  remov- 
ing from  the  damp  closet  at  24  hours'  age. 

4.  Xormal  treatment. 

Two  brands  of  well-known  cement  of  high  quality  were  run  in  parallel. 
The  mortars  were  of  proportions  1 :3,  Ottawa  sand  being  used.  The 
results  obtained  are  summarized  below : 


188 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


TABLE  2 
Effect  of  Cold  Storage  on  Strength 


Cement 

Mix 

Temper- 
ature of 
storage 
water, 
deg.  F. 

Storage 
method 

Strength,  pounds 
per  square  inch 

Per  cent  of  loss 

Number  of 
specimens 

7  days 

28  days 

7  days 

28  days 

X 

Neat 

60 

Normal 

735 

739 

0 

0 

10-12 

43 

1 

606 

693 

18 

6 

12-12 

42 

9 

654 

735 

11 

0 

12-12 

60 

Normal 

702 

745 

0 

0 

24-24 

34 

3 

638 

665 

9 

11 

24-23 

X 

1  :3 

60 

Normal 

300 

361 

0 

0 

11-12 

43 

1 

281 

361 

6 

0 

11-11 

42 

2 

283 

371 

6 

+3 

11-11 

60 

Normal 

313 

408 

0 

0 

24-24 

34 

3 

262 

312 

16 

24 

22-24 

Y 

Neat 

60 

Normal 

628          843 

0 

0 

12-12 

4:> 

1 

650          770 

+3 

9 

12-12 

44 

2 

649 

872 

+3 

-1-4 

12-12 

60 

Normal 

628          697 

0 

0 

24-24 

34 

3 

530          622 

16 

11 

22-24 

Y 

1:3 

60 

Normal 

250 

350 

0 

0 

12-12 

43 

1 

253 

370 

+1 

4-6 

12-11 

44 

2 

287 

327 

+  15 

+7 

12-12 

60 

Normal 

228 

317 

0 

0 

22-24 

34 

3 

197 

234 

14 

26 

22-24 

From  these  results,  it  is  safe  to  conclude  that,  aside  from  the  effects  of 
frost,  low  temperatures  are  adverse  to  the  development  of  the  hardening 
process  in  cement,  and  that  in  general  this  effect  is  more  pronounced  in 
mortars  than  in  neat  cement. 

The  adsorption  of  calcium  hydroxide  by  the  complex  hydrogel  may 
proceed  at  a  lower  rate  at  lower  temperatures;  or  if  this  is  not  so,  the 
primary  hydration,  of  which  this  hydrogel  is  the  product,  may  proceed 
more  slowly,  and  thus  less  of  the  hydrogel  be  produced, — either  of  which 
processes  will  detract  from  the  hydraulic  activities  of  the  mass.  It  would 
seem  from  the  experiments  that  the  latter  is  the  more  satisfactory  expla- 
nation, since  the  test  specimens  which  were  chilled  at  first  and  allowed 
to  return  to  normal  temperature  show  a  tendency  to  return  to  normal 
strength  at  the  longer  periods,  while  the  general  tendency  in  the  series 
kept  constantly  in  cold  water  is  to  fall  further  off  from  the  normal,  indi- 
cating only  a  limited  available  amount  of  hvclrosrel  to  undergo  the  coa^Ti- 

O  •/  */  C_?  o  C"1 

latin g  process. 


PACINI,   METAMORPHI8M   OF  PORTLAND   CEMEXT  189 

The  effect  of  sudden  chilling  at  a  period  when  a  large  proportion  of  the 
strength  is  already  developed  does  not  show  any  decided  direction,  both 
the  positive  and  negative  variations  from  the  normal  averaging  the  same. 
It  may  therefore  be  concluded  that,  for  the  temperatures  studied,  a  chill- 
ing of  this  kind  has  no  significant  effect. 

An  explanation  according  to  the  crystallization  theory  of  hardening 
would  fail  to  fit  the  facts  so  satisfactorily.  In  the  specimens  that  were 
chilled  at  first  and  allowed  to  return  to  normal  temperature,  there  should 
be  under  this  hypothesis  a  more  significant  decrease  of  strength,  owing 
to  the  formation  of  small,  non-cohesive  crystals  from  the  rapid  tempera- 
ture change.  The  return  to  normal  conditions  should  not  favor  so  nearly 
complete  a  recuperation  as  has  been  noted;  unless  a  re-solution  of  the 
crystals  and  recrystallization  were  supposed,  in  which  case  it  may  be 
argued  that  such  a  process  would  require  an  abnormal  solubility  of  small 
crystals  when  compared  with  large.  In  a  normal  specimen,  re-solution 
and  recrystallization  are  undoubtedly  going  on,  strengthening  the  struc- 
ture, and  the  large  crystals  are  growing  at  the  expense  of  the  small.  If 
small  crystals  preponderate  at  seven  days'  age,  resulting  in  a  weak  mass, 
it  is  necessary  to  postulate  a  comparatively  high  solubility  of  the  small 
crystals  in  order  to  arrive  at  a  normal  strength  at  28  days.  This,  while 
by  no  means  impossible,  is  not  probable. 

Turning  to  the  specimens  kept  continuously  in  cold  water,  it  would 
seem  that,  although  the  first  chilling  should  show  severe  effects,  as  it  did, 
there  should  not  be  such  a  falling  off  in  the  rate  of  hardening,  if  the 
crystallization  be  progressive.  It  is  quite  possible,  however,  that  crys- 
tallization at  this  temperature  is  not  favored,  and  that  the  total  number 
of  binding  crystals  of  calcium  hydroxide  is  therefore  less  than  at  normal 
temperatures. 

QUANTITY   OF  WATER  AT   FIBST  ADDED 

Size  of  cement  particles. — Other  factors  being  equal,  the  amount  of 
cement  rendered  inert  by  the  action  of  water  is  proportional  to  the  per- 
centage of  fine  particles.  This  is  an  absolute  condition  and  presupposes 
free  access  of  water  to  every  particle.  Xeedless  to  say,  in  practice  this 
condition  is  seldom  realized,  except  approximately  in  laying  concrete 
under  water,  or  in  the  careless  use  of  an  excess  of  water  in  mixing,  or  in 
protracted  mixing. 

In  the  use  of  a  very  fine  cement,  then,  if  the  proper  proportion  of 
water  is  added,  the  mixing  time  carefully  regulated  and  proper  precau- 
tions taken  in  depositing,  the  influence  of  texture  upon  the  strength  of 
the  mass  occasioned  bv  the  action  of  water  is  reduced  to  a  small  quantity, 


190  AXNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

by  virtue  of  the  greater  hydraulic  activity  of  the  fine  particles,  increasing 
the  impermeability,  as  will  be  shown,  and  the  confining  therefore  of  the 
action  of  the  excess  water  to  a  narrow  zone.  The  bulk  of  the  cement  will 
be  properly  hydrated  in  spite  of-  the  fineness. 

The  investigation  of  the  effect  of  the  size  of  particles  due  to  the  action 
of  water  thereon  alone  is  not  feasible,  because  no  satisfactory  measure  of 
laitance  formation,  except  the  strength  of  the  mass,  has  been  devised. 
The  measure  of  the  strength  would  be  unsatisfactory,  since  the  propor- 
tion of  fine  particles  affects  the  strength  in  other  ways  than  through  the 
formation  of  laitance,  as  has  been  pointed  out  in  a  previous  communica- 
tion. 

From  a  study  of  the  hydraulic  properties  of  reground  cement,  Spack- 
mann  and  Lesley  conclude  (93)  that  only  the  very  fine  flour  in  cement, 
that  portion  not  measured  by  the  present  tests  using  sieves,  reacts  when 
gaged  with  water  and  gives  strength.  It  is  difficult,  of  course,  to  draw  a 
sharp  dividing  line  between  active  and  inactive  material  in  cement,  al- 
though it  must  be  admitted  that  the  greater  part  of  the  coarse  material, 
even  though  it  be  of  the  same  chemical  composition  as  the  fine,  has  little 
or  no  cementing  value  and  serves  mainly  as  a  filler. 

Suitable  fractional  separation  of  the  portion  of  cement  passing  the  200 
sieve,  by  air-elutriation  or  other  method,  should  with  careful  study  be  a 
valuable  guide  to  the  most  efficient  mechanical  composition.  Experi- 
ments upon  the  first  method  of  separation  are  recorded  by  Peterson  (71), 
and  a  scientific  method  of  fractional  elutriation  using  an  inactive  liquid 
has  been  worked  out  by  Thompson  (100).  Much  should  be  gained  by 
the  application  and  development  of  these  methods.  The  influence  of  the 
size  of  particles  of  inert  material  added  to  the  cement  is  also  of  great 
consequence,  and  a  proper  mechanical  grading  of  the  sand  used  in  mor- 
tars is  recognized  as  vital.  The  presence  of  clay  in  this  sand,  or  the 
addition  of  clay  alone  to  cement,  come  under  this  category,  and  have 
occasioned  a  great  deal  of  discussion  (8,  32,  33,  110). 

A  comparison  was  made  of  the  permeability  of  1 :4  mortar  of  Portland 
cement,  when  used  in  its  ordinary  condition,  and  when  screened  through 
a  number  200  sieve. 


P  AC  IS  I,    METAMORPHI8M    OF   PORTLAND    CEMENT 


191 


TABLE  3 
Permeability  of  2-inch  Cubes,  Age  28  Days,  Subjected  to  80  Ibs.  Pressure 


Cement 

Temperature 
of  water. 
Deg.  Fahrenheit 

Grams  of  water  passing 
per  hour 

Number  of 
testa 

Unscreened 

Screened 

A  

66        68 
68      68 
68      68 
68      68 
64       64 
64       64 
64      64 
68       72 
68      68 

22 
25 
29 
331 
27 
31 
5 
6 
71 

33 
2 
Trace 
81 
Trace 
2 

0 

Trace 
0 

5,   6 
6,    6 
6,  6 
5,  6 
5,  6 
6,   6 
3,  6 
5,  6 
6,  6 

B 

c 

D 

E 

F  

G             

H.. 

i  :::::. 

A.verao'e 

61 

13 

The  marked  decrease  in  permeability  resulting  from  the  use  of  finer 
cement  in  mortar  demonstrates  that  in  impermeability,  as  in  strength, 
the  finest  particles  are  the  most  active  factors. 

Mechanical  agitation  irlien  irate r  i*  added. — Increased  working  should 
weaken  a  cement  after  a  certain  maximum  point  is  passed.  In  order  to 
•establish  this  point,  the  effect  of  prolonged  working  was  investigated. 
It  was  necessary  to  use  a  mix  of  fluid  consistency,  in  which,  for  obvious 
reasons,  the  final  set  would  not  under  normal  conditions  take  place  dur- 
ing the  time  over  which  the  experiments  were  extended. 

Two  grouts  were  employed:  one  in  which  cement  was  mixed  with  30 
per  cent  of  its  weight  of  water,  and  one  in  which  an  equal  weight  of 
water  was  used.  The  different  tests  were  run  respectively  for  periods 
from  one  minute  to  five  hours,  and  they  were  mixed  in  a  motor-driven 
stirring  machine  of  the  type  common  in  chemical  laboratories. 

After  the  stated  period  of  stirring,  the  grouts  were  poured  into  glass 
tubes  and  kept  in  a  damp  closet  for  the  twenty-eight-day  period.  Cylin- 
ders exactly  two  diameters  high  were  cut  from  the  specimens  and  crushed 
in  the  compressing  machine,  two  cylinders  being  crushed  for  each  period, 
and  the  average  of  the  cornpressive  strengths  being  recorded. 


192 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


TABLE  4 
T-wenly-eiglit-day  Tests  of  Grouts  Mixed  for  Varying  Lengths  of  Time 


Duration  of  mixing 

Compressive  strength,  pounds 
per  square  inch,  average 
of  duplicate  te&ts 

50  per  ct  grout 

100  per  ct.  grout 

1  lllinilte 

5240 
5545 
5710 
5875 
6075 
4775 

3095 
4725 

4955 
4840 
4320 

4538 

15  minutes 

30  minutes              . 

1  hour 

2  hours 

5  hours           . 

The  effect  of  mechanical  agitation,  when  thus  prolonged,  is  equivalent 
to  that  of  the  use  of  excess  water — the  strength  of  the  cement  is  pro- 
gressively diminished  as  the  working  proceeds.  It  is  noteworthy  that 
the  effect  is  only  reached  after  a  certain  optimum  period  is  passed.  Be- 
fore this  time,  increased  working  increases  the  strength.  We  may  con- 
clude that  there  occurs  within  this  period  a  process  which  neutralizes  the 
effect  of  hydrolysis;  and  this  process  is  probably  the  formation  of  the 
network  which  constitutes  the  setting. 

As  will  be  seen  later,  the  effect  of  excess  water  is  to  reduce  the  ulti- 
mate strength.  The  effect,  then,  of  mechanical  agitation  must  be  to 
bring  more  cement  into  contact  with  water  and,  therefore,  to  increase 
hydrolysis.  This  is  probably  accomplished  by  stripping  off  the  protective 
film  of  gelatinous  material  which  envelops  each  cement  particle  when  it 
comes  into  contact  with  water,  which  film  regulates  the  hydration  of 
cement  and  causes  it  to  proceed  in  a  regular  manner.  This  film  being 
stripped  off,  the  cement  is  subject  to  the  destructive  action  of  hydrolysis. 

Where  more  water  is  originally  present,  the  destructive  action  is  sooner 
attained,  as  will  be  seen  by  comparing  the  100  per  cent  grout  with  the 
50  per  cent.  Evidently,  the  setting  process  proceeds  best  at  high  concen- 
trations, when  the  amount  of  water  is  low.  This  may  be  so  regulated 
that  the  setting  process  will  not  take  place  at  all,  by  using  a  large  excess 
of  water  and  much  mechanical  agitation,  as  has  been  repeatedly  observed, 
by  the  writer. 

Setting  time  of  cement  in  laboratory  air  and  in  damp  closet. — The 
standard  specifications  for  setting-time  tests  call  for  storing  the  specimen 
in  the  damp  closet,  whereas  the  tests  as  generally  conducted  in  most 
laboratories  are  made  in  the  open  laboratory  air.  A  series  of  experi- 
ments was  made,  for  the  purpose  of  noting  the  deviation  from  standard 
results  caused  by  this  departure  from  the  rule. 


PACIXI,   METAMORPHI8M    OF  PORTLAND    CEMENT 


193 


TABLE  5 
Setting  Time  in  Laboratory  Air  and  in  Damp  Closet 


Cement 

Time  of  set  in  minutes 

Laboratory  air 

Damp  closet 

Initial 

Final 

Initial 

Final 

x 

255 
120 
300 
240 
240 

375 
360 
420 
360 
390 

300 

300 
360 
285 
250 

435 

450 
480 
420 
450 

Y-l  . 

Y-2  

Y-3  

Y-4  

From  these  results,  it  will  be  seen  that  setting  in  a  relatively  dry- 
atmosphere  takes  place  in  a  shorter  time  than  in  a  damp  one;  also  that 
the  setting  time  is  more  uniform  under  conditions  of  high  atmospheric- 
humidity. 

At  the  same  temperature,  evaporation  takes  place  more  rapidly  in  the 
former  case ;  and  allowing  a  cement  mix  to  stand  in  such  a  position  that 
evaporation  of  the  mixing  water  may  readily  take  place  is  practically 
equivalent  to  the  use  of  an  insufficient  amount  of  mixing  water. 

Effect  of  excess  of  mixing  water  on  strength  of  concrete. — Concrete  is 
often  mixed  so  wet  that,  as  it  is  filled  into  forms  to  a  depth  of  several 
feet,  the  water  rises  above  the  concrete  and  throws  out  considerable  lai- 
tance  from  the  cement.  The  ease  of  mixing  and  placing  very  wet  con- 
crete is  the  constant  incentive  for  its  use.  This  practice,  however,  is 
followed  by  a  great  deal  of  deterioration  of  the  concrete  in  strength. 

The  strength  rapidly  decreases  with  the  increase  in  the  quantity  of 
water  used  in  mixing.  The  visible  effect  of  this  weakening  is  the  forma- 
tion of  laitance,  which  has  little  or  no  setting  power  or  strength,  and 
which  represents  the  loss  of  an  active  part  of  the  cement,  since,  as  is 
recognized,  the  finer  parts  are  more  hydraulically  active. 

Tests  were  made  by  mixing  concrete  at  normal  consistency  and  shovel- 
ing one-half  the  batch  into  a  tank  containing  three  to  four  inches  of 
water,  the  depth  of  concrete  being  about  four  inches.  The  water  rose  to 
about  an  equal  depth  above  the  concrete.  In  test  Xo.  1,  the  concrete  was 
allowed  to  settle  in  water  four  inches  in  depth  for  30  minutes,  when  the 
excess  of  water  was  siphoned  off  and  the  remaining  material  poured  into 
molds.  In  test  Xo.  2,  the  depth  of  water  in  the  tank  was  three  inches, 
and  the  water  was  siphoned  off  immediately  while  in  agitation.  In  test 
Xo.  3,  the  same  process  was  repeated,  except  that  the  depth  of  the  water 


194 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


was  four  inches,  and  the  concrete  used  was  somewhat  leaner.  Test  No.  4 
represents  the  direct  qualitative  effect  of  the  addition  of  an  excess  quan- 
tity of  mixing  water  without  subsequent  handling.  All  specimens  were 
cylinders  six  inches  in  diameter  and  12  inches  high.  The  remainder  of 
the  batch  of  concrete  in  each  case  was  poured  directly  into  molds,  and  the 
specimens  were  broken  at  28  days.  The  amount  of  cement  lost  was 
roughly  ascertained  where  possible  by  filtering  the  siphoned  water  and 
weighing  the  amount  retained  on  the  filter. 

TABLE  6 

Effect  of  Excess  of  Mixing  Water  on  Strength  of  Concrete 


Test  No. 

No.  of 
specimens 

Proportions 

Per  cent 
of  water 

Strength  at  28 
days,  pounds 
per  sq.  in. 

Per  cent  of 
cement  lost 

1 

I5 

3 

2 

1:2:4 
1:2:4 

8.2 
8.2 

1240 
760 

2 

9  5 

M 

3 

2 

1:2:4 
1:2:4 

8.2 
8.2 

1485 
770 

io 

3 

35 

3 
3 

1  :  2.33  :  5 
1  :  2.33  :  5 

8.2 

8.2 

1490 
315 

12 

4 
4 

3 
3 

1:2:4 

1:2:4 

8.2 
10.3 

1385 
1155 

i 

5  Specimens  shoveled  into  water  as  described. 

Evidently,  then,  the  mere  presence  of  an  excess  of  water  is  sufficient  to 
produce  the  weakening  effect,  independently  of  any  actual  removal  of 
cement  from  the  concrete.  As  may  be  seen  from  Nos.  1  to  3,  the  leaner 
mixes  suffer  the  greater  deterioration  in  strength. 

Effect  of  excess  of  mixing  water  on  permeability  of  concrete. — A  par- 
allel series  of  tests  upon  the  permeability  of  concrete  treated  with  an 
excess  of  water  was  made,  in  which  the  correspondingly  numbered  speci- 
mens were  treated  in  the  same  manner.  The  cylinders  cast  from  these 
batches  were  eight  inches  in  diameter  and  six  inches  in  length,  and  were 
cased  in  the  standard  manner  for  permeability  tests.  Three  specimens 
were  made  for  each  test,  and  at  the  age  of  28  days  were  submitted  first  to 
40  pounds  pressure  for  one  hour,  then  to  80  pounds  for  one  hour,  without 
interruption.  The  flow  recorded  is  in  grains  passing  during  the  last  ten 
minutes  of  test. 


PACINI,   METAMORPHISM   OF  PORTLAND   CEMENT 


195 


TABLE  7 
Effect  of  Excess  of  Mixing  Water  on  Permeability  of  Concrete 


Test  No. 

Proportions 

Per  cent  of 
water 

Temperature 
of  percolating 
water 

Grams  passing  in  last 
ten  minutes 

40  pounds 

80  pounds 

1 
I6 

2 
26 

3 

4 
4 

1     2         4 

1     2         4 

1     2          4 
1     2          4 

1     2.33    5 
1     2.33    5 

1     2          4 
1     2         4 

8.2 
8.2 

8.2 

8.2 

8.2 
8.2 

8.2 
10.3 

67°  F. 

0 
479 

0 

212 

0 
1814 

38 
26 

0 
456 

0 

588 

21 
Not  tested 

18 
80 

58°  F. 

56°  F. 
60°  F. 

67°  F. 

6  Specimens  shoveled  into  water  as  described  above. 

In  the  foregoing  experiments,  the  decrease  in  strength  and  water- 
tightness  may  be  referred  to  the  deteriorating  influence  of  excess  water 
upon  the  cement  (16).  It  may  of  course  be  argued  that  the  more 
marked  effects  obtained  in  series  1,  2  and  3  than  in  series  4  are  due  to 
the  method  of  making  the  tests;  that  is,  that  a  considerable  proportion 
of  the  active  cement  was  actually  removed  from  the  body  of  the  concrete 
by  siphoning  off  the  supernatant  water  with  its  laitance. 

Effect  of  excess  of  mixing  water  on  the  strength  of  neat  cement. — 
With  the  idea  in  mind  that  the  weakening  effect  was  independent  of  the 
removal  of  cement  (1),  a  further  series  of  tests  was  instituted,  using  a 
neat  cement  of  good  quality.  The  cement  was  poured  into  a  series  of 
glass  tubes  in  which  increasing  proportions  of  water  had  been  put,  the 
tests  representing  a  series  of  grouts  mixed  respectively  with  50,  75,  100, 
150,  200  and  500  per  cent  by  weight  of  aement  of  water.  The  tubes  were 
shaken  for  one  hour  and  then  allowed  to  stand  for  28  days.  The  cement 
settled  into  the  bottom  of  the  tubes  in  the  order  of  its  coarseness,  the  fine 
nebulous  laitance  settling  last  as  a  cheesy  white  layer  of  increasing  thick- 
ness, as  the  percentage  of  water  was  higher.  This  layer  was  carefully 
trimmed  off  in  preparing  the  test  specimens. 

On  breaking  out  the  cylinders  from  the  tubes  at  the  end  of  the  test 
period,  it  was  decided  to  cut  each  cylinder  into  two,  each  exactly  one 
diameter  high,  carefully  noting  the  respective  position  of  each  in  the 
tube.  On  submitting  these  to  compression  it  was  seen  that  the  direction 
of  difference  between  the  upper  and  lower  layers  was  not  constant,  nor 


196 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


was  the  difference  a  significant  one,  so  that  it  was  considered  legitimate 
to  average  the  strengths. 

It  will  be  seen  by  the  table  below  that,  even  without  actual  removal  of 
any  cement,  the  formation  of  laitance  has  a  weakening  action  upon 
cement. 

TABLE  8 

Cotitpressive  Strength  of  Grouts  Mixed  icith  Varying  Proportions  of  Water 


Per  cent  of  water 

Crushing  strength, 
Ibs.  per  square  inch, 
average  of  two  tests. 

Age,  28  days 

50 

6855 

75 

5900 

100 

4500 

150 

3430 

200 

2960 

500 

1810 

The  effect  of  excess  of  mixing  water  is  therefore  seen  to  result  in 
decrease  of  strength  as  the  water  increases.  Whether  the  effect  is  a 
permanent  one  was  the  next  question  that  presented  itself.  To  settle 
this  point,  a  new  series  was  undertaken,  in  which  a  larger  number  of 
differing  percentages  was  introduced,  and  in  which  the  resulting  strength 
at  two  periods  was  determined. 

The  cement  was  mixed  with  the  stated  percentage  of  water,  and 
worked  for  two  minutes,  the  drier  mixes  upon  the  table  in  the  usual 
fashion,  and  the  wetter  mixes  merely  poured  into  the  tubes  and  shaken. 
Paper  mailing  tubes  were  used,  2  inches  by  48  inches,  treated  with 
molten  paraffin  and  sealed  with  paraffined  corks,  so  as  to  be  absolutely 
tight.  To  obviate  the  effect  of  possible  leakage,  the  whole  series  was 
stored  in  damp  sand. 

Cylinders  two  diameters  high*  were  cut  from  the  specimens  at  the 
stated  periods,  each  cylinder  being  cut  as  nearly  as  possible  the  same  dis- 
tance from  the  bottom,  and  care  was  taken  to  avoid  including  any  of  the 
soft  cheesy  top  portion,  the  settled  laitance. 


PACINI,   METAMORPHI8M    OF  PORTLAND    CEMENT 


197 


TABLE  9 
Compressive  Strength  of  Grouts  Mixed  with  Vaiying  Proportions  of  Water, 

Over  Extended  Period 
(Each  result  is  the  average  strength  of  three  specimens.) 


Compressive  strength,  pounds  per 

Percentage  of 

square  inch 

Per  cent  gain  in 
strength  over 

28  days 

3  months 

28  days 

22 

7076 

7504 

6 

25 

6174 

5402 

—13 

30 

4563 

6030 

32 

38 

3992 

5059 

27 

50 

2991 

5312 

77 

75 

2113 

4078 

93 

100 

1609 

3544 

120 

150 

1270 

2379 

87 

200 

1306 

2579 

97 

500 

399 

1141 

186 

It  is  apparent  from  these  figures  that  the  effect  of  hydrolysis  upon  the 
strength  of  cement  is  a  reversible  one,  at  least  to  a  certain  extent,  since 
the  specimens  in  which  an  excess  of  water  was  used  in  mixing  showed  a 
greater  recuperative  ability  at  the  longer  period  than  the  cement  in 
which  the  normal  amount  of  mixing  water,  in  this  case  22  per  cent,  was 
used. 

Upon  inspection,  it  was  observed  that  the  three  months'  specimens 
showed  in  each  case  much  less  laitance  than  the  similar  28  days'  speci- 
mens had  shown,  and  it  was  considered  probable  that  the  laitance,  in 
standing,  had  adsorbed  free  lime  from  the  remainder  of  the  cement, 
through  the  activity  of  the  water  permeating  the  mass,  and  thus  reverted 
to  the  original  condition  of  the  cement,  or  an  approach  thereto.  An 
analysis  was  accordingly  made  of  laitance  scraped  off  from  the  top  of  one 
of  the  500  per  cent  water  specimens  and  thoroughly  washed  by  decanta- 
tion.  It  probably  represents  a  maximum  condition  in  the  hydrolysis  of 
cement. 

TABLE  ]0 
Analysis  of  Laitance  from  500  per  cent  Specimen 


As  obtained  from 
specimen 

Treated  with  lime 
water 

Si02  .  . 

15.28 

15.91 

Fe,O, 

2  28 

2.42 

ALO,         ' 

3.98 

5.82 

CaO  .                                 

26.96 

36.67 

MgO.  . 

2.86 

1.28 

so3  :  

6.47 

2.72 

CO2   H2O   etc 

42.17 

35.18 

198  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

The  normal  ratio  of  silica  to  lime  in  unset  cement  may  be  considered 
1  to  2.82.  In  this  material  we  find  the  ratio  1  to  1.76.  This  indicates  a 
great  loss  of  lime;  and  it  was  thought  possible,  that,  by  adsorption  of 
lime,  this  laitance  might  regain  at  least  a  part  of  its  hydraulic  proper- 
ties. Accordingly  it  was  digested  for  several  days  with  lime  water  at 
laboratory  temperature,  filtered  off,  carefully  washed  with  distilled  water 
and  dried,  as  was  the  previous  sample,  at  100°  C.  An  analysis  showed 
the  results  tabulated  in  the  second  column.  The  ratio  of  Si02  to  CaO 
had  changed  to  1 :  2.30. 

Besides  direct  metathetical  reactions  between  the  components  of  ce- 
ment and  the  water  solution  which  always  surrounds  a  mass  of  hardening 
cement,  adsorption  of  various  materials  from  this  solution  is  unques- 
tionably always  going  on.  Were  the  fine  particles  of  cement  inert  chem- 
ically, this  would  still  take  place,  by  virtue  of  the  enormous  total  surface 
which  they  must  present.  Clay,  it  has  been  demonstrated,  has  the  prop- 
erty of  adsorbing  ions  of  C03  from  solutions  of  carbonates,  and  of  Cl 
from  solutions  of  chlorides  (10). 

The  laitance  then  may,  by  adsorption  of  calcium  hydroxide  given  off 
from  the  cement  adjacent  to  it,  recover  some  of  the  lime  lost  by  it. 
Whether  the  lime  adsorbed  restores  the  original  status  of  constitution  is 
of  course  mere  speculation.  The  trend  of  the  strength  tests  shows  that 
this  is  probably  not  so,  but  that  the  adsorption  is  not  entirely  a  reversion 
of  the  hydrolytic  reaction ;  in  other  words,  that  "drowned"  cement  will 
probably  never  recover  and  attain  to  the  strength  it  would  have  had  with 
proper  hydration. 

Effect  of  the  presence  of  clay  and  dissolved  substances. — It  is  apparent 
that  if  the  decreased  strength  be  directly  referable  to  the  action  of  the 
excess  water  upon  the  cement,  any  means  of  preventing  the  access  of 
excess  water  should  prevent,  if  only  to  a  degree,  the  destructive  action. 
The  colloidal  nature  of  clay  (6)  has  been  utilized  in  the  water-proofing 
of  concrete,  the  principle  of  its  action  being  the  formation  of  continuous 
gelatinous  films  throughout  the  structure,  which  prevent  the  passage  of 
water.  Although  the  same  problem  is  not  presented  in  a  grout  that  exists 
in  finished  concrete,  it  is  probable  that  some  blanketing  action  might 
occur  upon  the  addition  of  clay  to  the  mixed  mass. 

The  point  was  investigated.  To  correct  for  the  effect  of  absorption  of 
part  of  the  mixing  water  by  the  admixed  clay,  a  consistency  test  was 
made  upon  a  sample  of  cement  to  which  10  per  cent  of  clay  had  been 
added,  and  it  was  found  to  require  4  per  cent  more  water  than  the  same 
cement  used  neat. 

The  clay  mixes  were  accordingly  gaged  with  4  per  cent  more  water 


P ACINI,   METAMORPHISM   OF  PORTLAND   CEMENT 


199 


than  the  corresponding  neat  cement  mixes,  and  the  following  series  of 
compressive  tests  was  made : 

TABLE  11 

Effect  of  Clay  upon  Destructive  Action  of  Eacess  of  Mixing  Water 
(Average  of  two  tests  at  28  days) 


Neat  cement 

Cement,  10  per  cent  of  which  was 
replaced  by  a  fat  clay  (dried) 

Water, 
per  cent 

Compressive 
strength,  pounds 
per  square  inch 

Water, 
per  cent 

Compressive 
strength,  pounds 
per  square  inch 

50 

5782 

54 

1282 

75 

3134 

79 

1328 

100 

2273 

104 

2577 

150 

1896 

154 

2156 

200 

1381 

204 

1320 

500 

514 

504 

No  strength 

developed 

If  the  action  of  saline  solutions  upon  cement  is  to  accelerate  the  hy- 
drolysis of  the  latter,  it  would  appear  that  the  destructive  action  of  excess 
water  would  be  accelerated  by  the  presence  therein  of  saline  substances 
in  solution;  also,  it  is  legitimate  to  expect  that  the  addition  of  clay 
restraining  the  hydrolysis  due  to  excess  water  will  in  this  case  exert  a. 
similar  influence. 

The  following  experiments,  parallel  to  the  foregoing  ones,  elaborate 
this  point: 

TABLE  12 

Effect  of  Clay  upon  accelerated  destructive  Action  of  Mixing  Water  Containing 
5  per  cent  of  Magnesium  Sulphate 

(Average  of  two  tests  at  28  days) 


Neat  cement 

Cement,  10  per  cent  of  which  was 
replaced  by  a  fat  clay  (dried) 

5  per  cent  solution 
of  magnesium 

Compressive 
strength,  pounds 

5  percent  solution 
of  magnesium 

Compressive 
strength,  pounds 

sulphate, 

per  square 

sulphate, 

per  square 

per  cent 

inch 

per  cent 

inch 

50 

2196 

54 

2774 

75 

548 

79 

1608 

100 

1512 

104 

No  strength 

150 

556 

154 

200 

No  strength 

204 

«          « 

500 

No  strength 

504 

a          a 

200  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

From  these  two  series  of  experiments,  it  is  qualitatively  apparent  that 
the  presence  of  clay  does  prevent  a  certain  amount  of  hydrolysis.  From 
the  first  series,  it  is  seen  that  this  effect  only  begins  to  show  itself  as 
higher  percentages  of  water  are  present,  which  would  indicate  that  the 
clay  may  have  taken  up  much  more  water  than  the  constituency  test 
revealed,  and  that,  in  the  relatively  drier  mixes  with  clay,  the  cement 
suffered  in  strength  because  of  insufficient  water.  On  the  other  hand, 
experiments  at  this  laboratory  in  which  clay  was  used,  replacing  up  to 
10  per  cent  of  cement  in  normally  gaged  material,  showed  that  no  signifi- 
cant decrease  in  strength  was  thereby  obtained ;  hence  the  loss  in  strength 
in  the  54  and  79  per  cent  grouts  cannot  be  due  to  this  cause. 

It  is  more  probable  that  the  colloidal  nature  of  the  added  clay  is 
brought  into  play  more  effectively  at  the  concentrations  in  which  in- 
creased strength  is  observed,  and  that  the  latter  is  due  to  the  coagulation 
of  the  clay  by  electrolytes  adsorbed  at  this  optimum  concentration. 

The  same  result  would  obtain  w^here  additional  saline  material  has 
been  added  to  the  mixing  water,  as  in  the  series  where  a  5  per  cent  solu- 
tion of  magnesium  sulphate  was  used.  The  clay  here  prevents  the  accel- 
eration of  hydrolysis  by  the  magnesium  sulphate  through  adsorption  of 
part  thereof,  and  possibly  by  coagulating,  forming  an  impenetrable  bar- 
rier to  the  further  action  of  water  upon  the  remainder  of  the  cement. 

QUANTITY  OF  WATER  THAT  MAY   SUBSEQUENTLY   COME   INTO    CONTACT 
WITH   THE   SYSTEM 

Permeability. — The  solvent  effect  of  water  coming  into  contact  with 
cement  structures  is  best  studied  by  the  permeability  test.  This  consists 
in  forcing  water  through  a  mortar  or  concrete  at  a  known  pressure  and 
observing  the  amount  of  leakage  through  the  specimen.  In  detail,  the 
specimen  is  generally  made  up  in  the  form  of  a  cylinder,  and  this  is 
cased  with  a  thick  coating  of  neat  cement  on  all  sides  but  the  bottom. 
The  water,  under  pressure,  is  applied  on  the  full  cross-section  of  the 
specimen  and  forced  through,  dripping  from  the  bottom,  whence  it  may 
be  collected. 

With  neat  cement,  of  course,  this  method  is  inapplicable,  because  of 
the  density  of  the  material  and  the  consequently  enormous  pressure  nec- 
essary to  force  water  through  it,  and  moreover  because  of  the  mechanical 
difficulty  in  confining  the  water  strictly  to  a  passage  through  the  speci- 
men. The  specimens  tested,  then,  are  lean  mortars  and  concretes. 

Although  this  test  is  designed  to  ascertain  the  resistance  which  these 
materials  offer  to  the  flow  of  water,  it  is  evident  that  this  resistance  is 
not  a  constant  quantity  in  the  case  under  consideration. 


PACINI,   METAMORPHISM    OF  PORTLAND    CEMENT  201 

The  temperature  and  pressure  of  the  percolating  water  being  constant, 
the  flow  is  diminished  by  cementing  and  clogging,  and  increased  by  ero- 
sion and  solution;  the  quantity  of  water  flowing  through  the  mortar  or 
concrete  therefore  is  a  function  of  the  balancing  of  these  processes. 

Cementing  may  result  from  deposition  of  material  originally  in  solu- 
tion in  the  percolating  water,  or  dissolved  from  one  portion  of  the 
structure  and  deposited  in  another. 

Clogging,  similarly,  results  from  material  originally  in  suspension  in 
the  percolating  water,  and  deposited  in  the  pores  of  the  concrete,  or  from 
material  eroded  from  one  part  of  the  mass,  either  mechanically  or  as  a 
result  of  solution  of  the  attacking  portions,  and  deposited  in  another 
part. 

Erosion  per  se  is  a  negligible  factor;  that  is,  the  flow  of  pure  water, 
carrying  no  suspended  matter,  will  have  very  small  mechanical  effect 
upon  an  insoluble  material.  When  the  water  is  armed  with  suspended 
matter,  however,  its  corrasive  effects  become  proportionally  magnified. 

Solution  is  the  most  important  factor  in  the  process  of  percolation. 
Following  the  order  laid  down  by  Van  Hise  for  natural  rocks  (104,  p. 
536),  the  basic  materials  removed  are,  firstly,  the  alkalies  and,  secondly, 
the  alkaline  earths,  in  the  order  calcium,  magnesium.  Since  the  alkalies 
exist  in  cement  in  the  proportion  of  a  little  over  one  per  cent  and  are 
not  essential  to  the  hydraulic  properties  or  the  strength,  their  solution 
is  a  matter  of  little  consequence,  except  in  that  it  may  result  in  the  for- 
mation of  solutions  which  react  upon  the  lime  compounds  and  render 
their  solution  more  easy  of  accomplishment.  This  reaction  has  been 
considered  elsewhere.  The  removal  of  magnesium  compounds  proceeds 
at  a  lesser  rate,  although  there  is  a  greater  percentage  of  them  present; 
and  their  removal,  in  the  main,  may  be  dismissed  as  insignificant. 

Since  more  than  half  the  weight  of  fresh  cement  consists  of  lime,  and 
since  the  strength  of  cement  depends  for  the  greater  part  upon  calcium 
hydroxide,  whether  crystalline  or  adsorbed  by  colloids,  the  removal  of 
calcium  hydroxide  from  set  cement  is  the  factor  of  the  greatest  impor- 
tance. Considering  its  solubility  in  pure  water,  the  reversion  of  the 
hydroxide  to  the  crystalline  form  tends  to  diminish  its  solubility,  or 
from  the  other  standpoint,  its  adsorption  by  a  colloid  tends  to  remove  it 
from  the  solvent  action  of  water.  Unfortunately,  however,  it  must  be 
borne  in  mind  that  without  exception,  cement  structures  are  nowhere 
subject  to  the  action  of  pure  water  alone.  From  rain  water,  with  its 
appreciable  burden  of  dissolved  gases  and  atmospheric  salts,  to  the 
water  of  the  ocean  and  the  more  heavily  laden  rock  and  mine  waters, 
concrete  structures  are  everywhere  in  contact  with  saline  solutions  of 
varying  concentrations. 


202  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

The  effect  of  solution  in  percolation,  then,  is  to  a  small  degree  de- 
pendent upon  the  solubility  of  the  components  in  pure  water.  This  effect 
diminishes  as  time  goes  on,  because  of  the  reversion  of  the  soluble  ma- 
terial to  a  less  soluble  form  and  because  of  the  protection  afforded  by  the 
insoluble  portions  of  the  system  decreasing  the  exposed  area  of  soluble 
material.  The  washing  away  of  these  protecting  films  will  of  course 
neutralize  the  second  factor.  The  increased  solubility  of  the  components 
of  set  cement  in  solutions  of  various  electrolytes  is  the  more  important 
element  in  percolation.  Even  a  very  dilute  solution  may  have  tremen- 
dous total  solvent  power,  when  the  time  element  is  considered.  In  fact, 
it  may  be  that  the  action  of  a  dilute  solution  will  on  the  whole  exceed 
that  of  a  concentrated  solution,  by  reason  of  the  greater  cementing  and 
choking  action  of  the  latter,  tending  to  diminish  the  quantity  of  water 
that  may  come  into  contact  with  the  soluble  portions.  A  dilute  solution, 
therefore,  with  its  more  insidious  attack,  is  probably  more  to  be  feared  in 
the  end  than  the  strong  brine. 

Observation  of  the  behavior  of  concretes  and  mortars  during  the  per- 
meability tests  gives  a  clue  to  the  balancing  of  these  processes,  whether 
there  is  a  preponderance  of  cementing  and  clogging  on  the  one  hand,  or 
of  solution  and  erosion  on  the  other.  Attempts  were  made,  in  the  experi- 
ments noted  below,  to  study  chemically  the  reactions  involved,  by  peri- 
odical analyses  of  the  percolating  water.  To  this  end  nearly  four  hun- 
dred complete  analyses  of  the  effluent  water  were  made.  Upon  tabulation 
of  these  it  was  observed  that  any  deductions  based  upon  them  would  be 
inconclusive,  as  the  chemical  composition  of  the  effluent  water  repre- 
sented one  of  a  great  number  of  variable  factors  that  might  occur  at  any 
point  either  within  or  without  the  concrete.  The  single  qualitative 
generalization,  that  lime  was  removed  from  the  cement  at  a  diminishing 
rate,  is  the  only  permissible  conclusion  from  the  analytical  data. 

The  original  purpose  of  these  tests  was  to  ascertain  the  suitability  of 
various  aggregates  for  use  in  concrete,  with  reference  to  their  stability 
in  the  presence  of  percolating  water.  At  the  conclusion  of  the  series,  it 
was  found  that  the  effect  of  water  upon  the  various  aggregates  was  prac- 
tically negligible,  during  the  period  of  observation,  and  that  the  action 
had  been  confined  to  the  cement  of  the  mortar.  The  aggregates  had  been 
protected  from  the  action  of  water  by  the  cement,  it  being  probable,  how- 
ever, that  a  continuation  of  the  tests  would  have  revealed  the  action  of 
water  upon  these  rocks,  when  the  protective  influence  was  removed. 

A  series  of  sixteen  aggregates  was  used,  in  as  many  concrete  specimens. 
Since  it  is  not  the  purpose  of  this  report  to  discuss  the  relative  suita- 
bility of  these  materials  for  concrete  construction,  but  only  to  consider 


PACINI,   METAMORPHISM    OF  PORTLAND   CEMENT 


203 


the  action  of  the  water  upon  the  cement,  two  cases  alone  will  be  con- 
sidered. 

The  rock  was  crushed  and  screened  for  each  experiment  to  the  same 
average  effective  size,  corresponding  to  the  following  mechanical  analysis : 

TABLE  13 
Mechanical  Analysis  of  Aggregate  used  in  Permeability  Tests 


Sieve 

Square  mesh 
opening,  in  inches 

Per  cent  passing 

1% 

1.89 

100 

W 

1.58 

94 

1 

1.02 

59 

% 

.78 

32 

2A 

.59 

21 

2 

.48 

16 

3 

.30 

6 

4 

.22 

0 

The  sieve  ratings  are  based  on  diameters  of  spheres  of  equivalent  vol- 
ume to  the  largest  sized  stone  particles  that  will  pass. 

The  fine  aggregate  was  crushed  quartz,  the  standard  sand  formerly 
used  for  cement  testing,  passing  the  Xo.  20  and  retained  on  the  Xo.  30 
sieve.  The  cement  used  was  a  standard  Portland  of  high  quality. 

The  specimens  were  made  in  the  laboratory's  standard  form  for  per- 
meability test,  cylinders  eight  inches  in  diameter  and  six  inches  in  length, 
the  proportions  used  being  1 :  3.5 :  6,  this  being  found  the  richest  mix 
practicable  to  secure  the  porosity  required  for  the  test.  They  were  cased 
in  neat  cement,  and  connected  suitably  for  subjection  to  the  pressure  of 
the  city's  water  mains.  Each  specimen  was  protected  from  the  direct 
flow  of  the  water  by  a  layer  of  one  inch  of  clean  coarse  sand.  The  average 
pressure  for  the  period  of  observation  (52  weeks)  was  22  pounds.  The 
determinations  of  the  rate  of  leakage  were  made  weekly  at  first,  and  later 
every  two  weeks  until  the  end  of  the  test. 

The  data  appended  below  represent  observations  on  the  rate  of  percola- 
tion of  water  through  two  of  the  specimens  which  present  the  greatest 
interest  from  the  standpoint  of  this  paper,  this  flow  being  recorded  in 
grams  passing  in  ten  minutes.  The  aggregate  used  in  one  specimen  was 
a  hardened  neat  cement,  crushed  to  the  size  stated,  and  used  in  place  of 
the  rock  generally  employed  in  concrete.  The  parallel  specimen  selected 
for  comparison  was  one  in  which  the  aggregate  was  a  crushed  granite, 
which  showed  a  low  solubility  in  hydrochloric  acid  (2.66  per  cent  dis- 
solved in  one  hour's  treatment  with  1 :  1  HC1). 


204 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


Temperature  records  of  the  percolating  water  were  not  kept,  since  these 
tests  represent  a  part  of  a  larger  series  in  which  this  would  have  been 
impracticable.  The  other  aggregates  tested  showed  results  from  which  it 
was  quite  difficult  to  draw  any  legitimate  conclusions  as  to  the  relative 
: suitability  of  different  rocks  in  concrete  subjected  to  these  conditions. 

Concretes  containing  different  aggregates. — A  scries  of  tests  on  con- 
cretes made  up  of  different  aggregates  but  with  the  same  cements  gave 
results  which  may  be  tabulated  as  follows : 

TABLE  14 

in  Grams  of  Water  passing  in  10  Minutes  through  Concrete  Specimens 
subjected  to  continuous  Water  Pressure  for  52  Weel-s 


Grams  passing 

in  10  minutes 

Time 

Pressure, 
pounds  per 
square  inch 

Month 

Concrete  with 
aggregate  of 
crushed 
hardened 
neat  cement 

Concrete  with 
aggregate 
ot  crushed 
granite 

24  hours 

25 

January  — 

2111 

60 

1  week 

22 

February  .  . 

836 

31 

2  weeks 

22 

662 

26 

3 

20 

626 

40 

4 

25 

570 

60 

5 

22 

March  

603 

62 

6 

20 

530 

50 

7 

20 

1295 

38 

8 

25 

1127 

40 

10 

25 

April  

1310 

45 

12 

26 

870 

25 

14 

24 

May  

997 

36 

16 

24 

985 

28 

18 

20 

June  

973 

32 

20 

17 

639 

20 

22 

20 

792 

40 

24 

17 

July  

731 

36 

26 

22 

802 

43 

28 

26 

August  

800 

49 

30 

22 

78  1 

46 

32 

20 

September. 

763 

50 

34 

19 

115 

Trace 

36 

26 

October.  .  .  . 

105 

2 

38 

26 

107 

2 

40 

23 

November.  . 

110 

3 

42 

25 

93 

2 

44 

22 

December.  . 

75 

5 

46 

21 

70 

3 

48 

25 

80 

10 

50 

20 

January.  .  .  . 

73 

7 

52 

20 

78 

7 

PACINI,   METAMORPHISM   OF  PORTLAND   CEMENT  205 

Comparison  of  these  two  sets  of  figures  indicates  that  the  cement  of  the 
concrete  is  more  attacked  than  the  aggregate.  In  fact,,  the  flow  obtained 
in  this  specimen  was  the  highest  but  one  of  a  series  of  sixteen,  and  the 
total  lime  content  of  the  effluent  water  was  also  the  highest  but  one. 

The  visible  effect  upon  examination  of  the  interior  of  the  specimens 
was  a  bleaching  of  the  mortar,  with  evident  solution  of  the  cement.  The 
original  percentage  of  lime  in  the  mortars  was  12.8.  Analysis  of  mortar 
from  the  granite  specimen  showed  a  content  of  4.8  per  cent,  indicating 
that  nearly  two-thirds  of  the  lime  had  been  dissolved  out.  Further  evi- 
dence of  the  loss  of  lime  was  found  in  the  heavy  white  crust  which 
formed  on  the  exposed  bottoms  of  the  concrete  specimens  during  the  test. 
Small  stalactites,  quite  soft  to  the  touch,  were  abundant.  The  quantity 
of  this  deposit  was  not  visibly  different  in  the  different  tests. 

The  calculated  loss  in  lime  of  the  mortar  was  greater  than  the  loss 
computed  from  periodical  chemical  analyses  of  the  effluent  water,  and 
this  is  due  to  the  fact  that  much  of  the  dissolved  lime  was  deposited  upon 
the  bottoms  of  the  specimens  as  the  stalactitic  growth  above  mentioned. 

There  was  no  evidence  that  suspended  impurities  in  the  water  had 
been  carried  into  the  interior  of  the  concrete,  and  it  is  therefore  supposed 
that  the  one-inch  layer  of  sand  by  which  the  latter  was  screened  from 
the  direct  flow  of  the  water  was  an  efficient  filter  for  the  purpose.  The 
clogging  action  resulting  from  this  source  may  therefore  be  dismissed  as 
negligible. 

It  may  be  concluded  from  these  tests  that  concrete  of  this  density  tends 
to  protect  itself  automatically  from  the  action  of  percolating  water,  so 
that,  for  the  period  investigated  at  least,  the  flow  tends  to  diminish  to  a 
minimum.  The  action  of  the  water  seems  to  be  confined  to  the  cement 
of  the  mortar,  leaving  the  aggregate  relatively  unaffected. 

It  is  evident  that,  notwithstanding  the  utmost  precaution  in  mixing 
concrete  test  specimens,  wide  differences  in  permeability  niay  obtain  in 
specimens  mixed  under  the  same  conditions  of  handling  and  by  the  same 
workman,  owing  to  structural  differences  in  the  resulting  mass.  How- 
ever, the  results  obtained  are  fairly  comparable. 

The  most  sensitive  test  for  the  internal  changes  which  the  concrete  has 
undergone  during  percolation  is  the  resulting  strength  of  the  concrete. 

Concretes  containing  different  cements. — A  series  of  tests  was  under- 
taken in  which  the  specimens  were  made  up  in  the  same  proportions, 
1 :  2.5 :  6,  using  in  each  specimen  the  same  coarse  aggregate,  a  crushed 
granite,  and  the  same  fine  aggregate,  a  standard  quartz,  but  using  differ- 
ent brands  of -cement.  The  specimens  were  stored  in  damp  sand  for  a 
period  of  28  days,  then  subjected  to  continuous  water  pressure  of  about 


206 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


25  pounds  for  a  period  of  11  months.  Parallel  specimens  were  stored  in 
damp  sand  during  this  period  and  allowed  to  attain  their  full  normal 
strength.  The  table  following  shows  the  leakage  and  final  strength  of 
the  specimens: 

TABLE  15 

Percolation  through  Concrete  Specimens 


Months  of  percolation 

Brands  of  cement  and  grams  of  water  passing  in  10  minutes 

A 

B 

c 

D 

E 

F 

K- 

146 
155 
56 
37 
72 
71 
68 
57 
40 

286 
125 
70 
47 
28 
12 
28 
46 
43 

7 
13 

63 
22 
90 
52 
37 
31 
34 
14 
12 

'io 

10 

164 
179 
167 
161 
65 
15 
11 
6 
2 

5 

1 

76 
16 
11 
11 
7 
17 
26 
16 
5 

'i 
2 

230 

82 
85 
82 
45 
39 
33 
21 
11 

14 

19 

1.  .  . 

2 

3  .  .  .  . 

4  

5  

6  

7  

8  

9  

10  

13 

8 

11  

TABLE  16 
Comparison  of  Strength  before  and  after  Permeability  Test 


A 

B 

c 

D 

E 

F 

Compressive  strength   of  specimens 
at  the  end  of  period  

7707 

490 

640 

890 

750 

590 

Compressive  strength    of   untreated 
specimens,  pounds  per  square  inch.. 
Loss  of  strength  through  percolation 
(per  cent) 

1080 
99 

1210 
60 

1230 

48 

1125 
21 

1220 

39 

1090 

46 

7  One  specimen  crushed.     Other  results  are  average  of  two  specimens. 

Effect  of  the  direction  of  flow  through  concrete. — Concrete  seems  to 
offer  less  resistance  to  the  flow  of  water  when  the  direction  of  the  flow  is 
parallel  to  the  bed  than  when  at  right  angles  to  it.  A  test  covering  this 
point  was  made  with  8-inch  cubes  of  concrete  of  the  proportions  1:4:14, 
fine  and  coarse  aggregate  being  a  standard  crushed  Milestone. 


PACIXI,   METAMORPHI8M   OF  PORTLAND   CEMENT 


20' 


TABLE  17 
Rate  of  Flow  in  Gallons  per  Square  Foot  per  Hour  under  20-ineli  Head 


Age  of  specimens,  67  days. 
Temperature  of  water,  64°  F. 

In  specimen  parallel  to 
bed 

In  specimen  perpendicular 
to  bed 

1st  2  minutes  

740.96 
585.28 
636.31 
535.53 
549.10 

mmersed  24  hours,  then  r 

665.38 
642.77 
662.80 
641.15 
659.57 

164.14 

159.54 
163.49 
158.33 
157.93 

tested  : 

182.46 
177.54 
177.54 
177.06 
173.67 

2d          "          

3d           " 

4th        "          

5th         " 

Specimens  i 

1st  2  minutes  

2d          " 

3d 

4th        "          

5th 

In  denser  concretes,  this  effect  was  not  found  so  marked.  It  will  be 
noted  that  after  storage  following  the  first  exposure  to  the  effect  of  per- 
colating water,  these  specimens  appear  to  offer  less  resistance  to  the  flow 
of  water.  This  may  be  due  to  the  fact  that  in  lean  concretes  the  propor- 
tion of  capillary  and  subcapillary  voids  is  smaller  and  that  of  super- 
capillary  voids  greater,  and  that  cementing  and  clogging  actions,  which 
have  their  greatest  effect  in  capillary  and  subcapillary  passages,  are  not 
so  effective. 

The  greater  flow  along  the  bedding  planes  has  been  observed  in  the 
•case  of  rock,  and  is  in  all  respects  a  phenomenon  of  the  same  nature.  In 
the  case  of  a  stratified  sandstone  cited  by  King  (51),  the  reason  is  ad- 
vanced that  no  more  water  can  pass  the  more  open  layers,  when  advancing 
-across  the  bedding  planes,  than  was  able  to  pass  those  of  the  closest  tex- 
ture ;  whereas  when  the  flow  is  along  the  bedding  planes,  each  particular 
.stratum  carries  water  in  proportion  to  the  coarseness  of  its  texture, 
uninfluenced  by  any  other. 

In  the  case  of  water  percolating  into  a  concrete  tunnel  this  would 
tend  to  emphasize  lateral  percolation,  and  in  the  case  of  disintegration 
would  exercise,  in  general,  a  localizing  influence.  It  is  not  to  be  as- 
sumed that  this  is  a  rigid  rule,  inasmuch  as  a  large  number  of  factors, 
evidently,  may  neutralize  this  influence. 

From  these  considerations,  it  will  be  seen  that  the  solvent  effect  of 
water  upon  set  cement  is  of  high  importance  in  considering  the  perma- 
nence of  concrete  structures,  and  that  this  solvent  effect  tends  to  diminish 
.as  the  set  cement  ages.  This  is  not  the  onlv  wav,  of  course,  that  water 


208 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


may  afterwards  affect  the  metamorphism  of  cement.  It  has  been  pointed 
out  by  Goldbeck  (43)  and  by  White  (108)  that  the  expansion' or  con- 
traction of  concrete  depends  upon  whether  the  concrete  remains  wet  or 
dry,  and  that  the  strains  caused  by  alternate  wetting  and  drying  of  con- 
crete may  be  a  more  fruitful  cause  of  cracks  than  temperature  changes. 
The  presence  of  an  optimum  quantity  of  water  is  necessary,  however, 
so  that  the  proper  reactions  take  place  in  the  mass  of  setting  cement,  in 
order  that  the  strength  may  increase  normally. 


QUALITY   OF   WATER  AT   FIRST  ADDED 

Cornpressive  strengths  of  neat  cements  gaged  ivitli  various  solutions. — 
A  normal  Portland  cement  was  mixed  with  the  proper  quantity  of 
water  (21  per  cent  by  weight)  in  which  was  dissolved,  in  the  different 
tests,  varying  concentrations  of  the  salts  indicated  in  the  subjoined  table. 
The  cement  was  worked  for  one  minute,  and  the  plastic  mass  was  tamped 
into  glass  cylinders  approximately  one  inch  in  diameter,  with  the  utmost 
precaution  to  avoid  all  air  bubbles  and  at  the  same  time  to  subject  all 
specimens  to  the  same  pressure. 

TABLE  18 

Compressi'veJStrenfftTis  of  Neat  Cement  Mixed  iritli  Solutions  of  Various  Salts 
(Age  of  specimens,  28  days.     Average  of  two  determinations) 


Mixes 

Pounds  per 
square  inch 

Gain  or  loss, 
per  cent 

1    Distilled  water 

7330 

2.  25%  rock  water8  diluted  with  distilled  water  
3.  50%        do. 
4.  75%         do.                                                           
5    Rock  water  alone 

6340 
6495 
6870 
5605 

-14 

-11 

-  6 
—23 

6      2%  sodium  chloride  solution 

6675 

g 

7.     4%         do 

5815 

-21 

8      6%         do 

5065 

—  31 

9.     8%         do.                                   

4215 

—43 

10    10%         do 

5285 

—29 

11.  Saturated  solution  of  calcium  sulphate  (±  0.2%  )  . 
12.  0  '2%  solution  of  calcium  chloride 

7025 
6960 

4 

13    02%  solution  of  magnesium  sulphate 

6680 

—  9 

14.  0.2%  solution  of  magnesium  chloride  
15.  Equal  parts  of  11  and  12  (CaSO4  and  CaCl2)  
16.  Equal  parts  of  13  and  14  (MgSO4  and  MgClj  
17.  Equal  parts  of  12  and  13  (Ca012  and  MgSO4)  
18.  Equal  parts  of  11  and  14  (  CaSO4  and  MgCl2)  

5595 
6565 
7355 
5810 
6200 

-23 
-10 
+0.6 
-21 

—15 

8  This  water  contained:   CaO.   1177   parts   per   million. 
MgO,    226 
S03,       408 
Cl,       4360 


PACINI,   METAMORPHISM    OF  PORTLAND    CEMENT  209 

The  glass  cylinders  containing  the  cement  were  then  stored  in  a  damp 
closet  for  28  days,,  when  the  cylinders  were  broken  out,  and  two  speci- 
mens, each  exactly  one  diameter  high,  cut  from  each  cylinder.  These 
were  put  into  water  for  a  few  hours,  so  that  they  might  be  in  the  moist 
state  when  crushed.  The  cylinders  were  kept  in  the  damp  closet  instead 
of  being  stored  under  water,  to  avoid  leaching  out  the  salts  contained  in 
the  mixing  water,  thus  obtaining  the  maximum  effect  of  the  dissolved 
salts. 

It  will  be  noted  that  there  is  a  decided  loss  of  strength  in  all  but  one 
case  (number  16).  This  particular  case  may  be  explained  by  the  prob- 
able formation  of  an  oxychloride,  by  the  magnesium  chloride  and  the 
magnesium  hydroxide  liberated  by  the  action  of  the  magnesium  sulphate 
upon  the  calcium  hydroxide  of  the  cement.  The  oxychloride  formed 
from  these  two  materials  has  a  tensile  strength  far  superior  To  that  of 
Portland  cement  itself,  and  its  presence  probably  counteracted  the  de- 
structive action  of  the  salts  upon  the  cement.  It  is  probable,  however, 
that,  at  longer  periods,  this  increase  would  disappear  and  become  a  de- 
crease. Otherwise,  the  presence  of  saline  matter  dissolved  in  the  mixing 
water  seems  to  have  a  decided  deleterious  effect  upon  the  strength  of 
cement.  This  point  is  of  marked  importance  in  construction,  inasmuch 
as  the  problem  of  mixing  water  is  often  solved  by  using  the  water  nearest 
at  hand,  without  inquiry  into  its  qualities. 

It  is  the  custom  to  specify  that  the  water  used  in  mixing  concrete  shall 
be  free  from  oil,  acid,  strong  alkalies  or  vegetable  matter  (77)  ;  but  such 
a  specification  does  not  cover  the  case  in  point,  and  the  presence  of  large 
quantities  of  dissolved  salts  in  water  used  for  construction  is  easily  over- 
looked. In  concrete  construction,  it  is  of  the  utmost  importance  that  the 
water  which  may  be  used  in  mixing  be  additionally  subjected  to  such 
tests  as  will  reveal  either  its  mineral  content  or  its  action  when  mixed 
with  cement  and  possible  subsequent  attack  thereon. 

The  action  of  sodium  chloride  appears  to  be  nearly  directly  propor- 
tional to  the  amount  employed.  This  salt  is  used  in  mixing  water  for 
construction  carried  on  in  cold  weather,  in  order  to  prevent  freezing  of 
the  deposited  concrete.  Its  effect  upon  the  strength  of  cement,  if  used  in 
excessive  quantities,  is,  as  has  been  shown  above,  likely  to  become  a  seri- 
ous matter.  Under  the  conditions  of  construction  which  generally  pre- 
vail, however,  much  of  the  salt  may  be  leached  out  of  the  mass.  The 
results  above  represent  a  condition  of  maximum  attack. 

Dieckmann  (25)  recommends  the  use  of  from  1  to  2.5  per  cent  of  salt 
for  concrete  to  be  laid  in  cold  weather,  but  states  that  percentages  larger 
than  this  cause  a  marked  decrease  in  the  strength. 


210 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


Effect  of  gaging  with  various  solutions  upon  the  strength  of  mortars 
afterward  stored  in  water. — The  above  tests  do  not  show,  of  course,  a 
normal  condition,  since  no  water  came  into  contact  with  the  cement 
after  it  had  set.  Working  with  more  porous  material,  a  1 :  3  mortar,  so 
that  in  storage  a  heightened  subsequent  water  action  might  take  place, 
the  following  results  were  obtained : 

TABLE  10 

Effect  of  various  Salts  dissolved  in  tlie  Mixing  Water,  upon  tlie  Strength  of 

1:3  Mortar 

(Sand,  screened  Cow  Bay.    Specimens  stored  in  damp  closet  for  24  hours,  then 
continuously  in  water  for  the  rest  of  period) 


Mixes 

Compressive  strength, 
pounds  per  square  inch 

Number  of 
specimens 

7  days 

28  days 

3  months 

Water  

815 
1005 
945 
1010 
885 
910 
865 
935 
1090 
930 
840 
1105 
1000 

1475 
1185 
1310 
1520 
1240 
1625 
1410 
1595 
1580 
1605 
1490 
1385 
1035 

2600 
1805 
2170 
2420 
2100 
2145 
2115 
2710 
2500 
2670 
2710 
2000 
1685 

1,3,3 
3,2,1 
3,3,3 
3,3,3 
1,3,3 
2,3,3 
2,3,3 
3,3,2 
3,1,2 
3,3,3 
2,1,1 
3,3,3 
2,3,3 

5,6,6 
6,6,6 
4,6,5 
6,6,6 
4,6,6 
3,6,6 
4,6,6 
2,5,6 
3,6,6 
5,6,6 
5,6,6 
6,6,6 
5,6,5 

I  %  solution  of  Ala(S04),  

2%        do.                          .... 

1  %  solution  of  Na2S04  

2%        do.                      

1  %  solution  of  MgS04  
1%        do.                     

1  %  solution  of  ZnS04 

2%         do.                      

1  %  solution  of  FeSO4  

2%        do. 

1  %  solution  of  NaCl 

2%        do. 

Tensile  strength,  pounds  per 
square  inch 

7  days 

28  days 

3  months 

Water.... 

179 
208 
193 
216 
205 
194 
185 
126 
205 
201 
184 
211 
224 

272 
272 
262 
290 
300 
260 
246 
263 
272 
266 
258 
261 
279 

326 
321 
340 
354 
343 
317 
283 
315 
319 
314 
311 
310 
310 

1  %  solution  of  A12  (SO4)3          

2%         do. 

1  %  solution  of  Na.2S04  

2%        do.                      

1  %  solution  of  MgS04 

2%        do. 

1  %  solution  of  ZnSO4 

2%         do. 

1  %  solution  of  FeSO4  
2%         do.                     

1  %  solution  of  NaCl  
2  %         do 

P ACINI,   METAMORPHI8M   OF  PORTLAND    CEMENT  211 

The  general  conclusion  that  may  be  drawn  from  these  values  is  that 
the  effect  of  electrolytes  in  the  mixing  water,  when  the  cement  is  after- 
wards subject  to  immersion  in  water,  is  to  increase  the  strength  at  the 
early  periods  (7  and  28  days),  but  later  to  depress  it  (15).  In  general, 
the  more  concentrated  solutions  give  a  greater  depression  of  strength. 
The  early  increase  in  strength  is  probably  due,  in  the  presence  of  an 
optimum  quantity  of  water,  to  additional  cementing  or  void-filling  ma- 
terial precipitated  in  the  pores  of  the  mortar  by  reaction  between  the 
added  electrolytes  and  the  solutions  resulting  from  the  action  of  water 
upon  cement.  This  deposited  material  may,  in  its  later  history,  revert 
to  a  soluble  form  and  be  washed  away,  leaving  abnormal  voids,  or  else 
in  its  growth  may  disrupt  the  cells  it  occupies,  in  either  case  reducing 
the  strength. 

Effect  of  gaging  grout  with  rock  ivaters. — In  grouting  deep  tunnels, 
the  question  has  arisen  as  to  the  advisability  of  using  the  rock  wrater  at 
hand  when  fresh  water  was  inaccessible.  The  water  available  in  the 
instance  in  hand  was  an  effluent  from  a  shale  bearing  a  small  proportion 
of  pyrites,  and  when  it  issued  from  the  rock  face  it  contained  a  quantity 
of  dissolved  hydrogen  sulphide.  As  none  of  the  water  was  immediately 
available  for  a  laboratory  test,  an  artificial  mixture  was  made  up,  in 
which  the  quantities  of  dissolved  salts  and  hydrogen  sulphide  occurring 
in  the  natural  water  was  purposely  exaggerated,  to  obtain  accelerated 
effects. 

TABLE  20 
Analysis  of  the  Artificial!!/  Mineralized  Water 

Parts   per  million 

H,S    '.        891 

CaO   1764 

MgO    1461 

SO3 1948 

Cl   2920 

A  grout  was  made  up  according  to  specifications,  using  a  normal  Port- 
land cement,  and  Cow  Bay  sand  with  100  per  cent  passing  10  sieve,  75 
per  cent  passing  40  sieve;  in  the  proportions  1:  iy2  with  35  per  cent  of 
liquid.  The  wet  mix  was  poured  into  glass  cylinders,  kept  24  hours  in 
air  until  set  had  developed  and  immersed  in  water. 

Four  sets  of  three  specimens  each  were  made,  the  first  set  mixed  with 
35  per  cent  of  distilled  water;  the  second,  35  per  cent  of  the  water  above 
mentioned;  the  third,  35  per  cent  of  a  10  per  cent  dilution  of  this  water, 
and  the  fourth,  35  per  cent  of  a  1  per  cent  dilution. 

Xo  discrepancy  was  observed  in  the  setting  time,  as  all  the  specimens 


212 


ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 


developed  a  fair  set  within  24  hours.  The  grouts  mixed  with  the  undi- 
luted sulphide  water  turned  a  dark  green,  but  otherwise  no  change  was 
noticed  in  these  or  any  other  specimens.  Three  cylinders  one  diameter 
high  were  cut  from  each  set  of  specimens,  and,  after  storing  28  days  in 
distilled  water,  were  crushed. 

TABLE  21 

Conipressive  Strength  of  Grout  Mixed  icith  Different  Proportions   of   Water 
Containing  Hydrogen  Sulphide 

(Average  of  three  specimens,  age  28  days) 

Pounds  pei- 
Mixes  square  inch 

Distilled  water 1424 

Undiluted  sulphide  water 1608 

10  per  cent  of  sulphide  water,  99  per  cent  of  distilled  water.  . . .     2088 
1  per  cent  of  sulphide  water,  99  per  cent  of  distilled  water 1110 

Apparently,  considering  the  average  of  the  last  three  values,  water  of 
this  composition  will  have  no  evil  effect  at  28  days  upon  the  grout  with 
which  it  is  gaged. 

Three  series  of  tests  were  undertaken,  in  which  a  1 :  3  mortar  of  Ot- 
tawa sand  and  a  cement  of  good  quality  was  mixed  with  Croton  water, 
and  with  two  typical  rock  waters  encountered  in  tunnel  work. 

TABLE  22 

Analyses  of   Rock   Waters 

Parts  per  million 
E  W 

CaO   85  943 

MgO 159  156 

SOS  ' 73  172 

Cl    1380  3420 

Total  solids  .  2978  7929 


The  normal  amount  of  water  was  used  to  mix  the  mortars  in  each 
case,  and  the  briquettes  were  stored  in  the  damp  closet  over  the  stated 
periods. 

TABLE  23 

Tensile  Strength  of  1:3  Mortars  Mixed  irith  Various  Saline  Waters 


Pounds  per  square  inch 

Number  of 
specimens  in 
average 

7  days 

28  days 

3  months 

Croton  water. 

302 
297 

296 

322 
343 

335 

344 
363 

383 

6,5,6 
6,6,6 
6,6,6 

Water  E  

Water  W  

PACINI,   METAMORPHIS1I   OF  PORTLAND    CEMENT  2lo 

As  was  found  in  the  case  of  the  grouts  last  mentioned,  waters  of  this 
general  concentration  do  not  appear  to  affect  the  strength  of  cement 
mortars  with  which  they  are  gaged,  and  the  probabilities  are  that  no 
serious  effects  will  result  from  this  cause  alone. 

QUALITY  OF  WATER   THAT  MAY   SUBSEQUENTLY   COME  INTO    CONTACT 
WITH  THE  SYSTEM 

Theoretical  considerations. — The  action  of  dissolved  salts  in  water 
that  comes  into  contact  with  concrete,  where  such  action  is  deleterious 
to  the  concrete,  has  been  carefully  studied  by  a  large  number  of  investi- 
gators (68,  81,  96,  112).  Of  the  salts  which  have  been  found  injurious, 
magnesium  sulphate  and  magnesium  chloride  seem  to  have  the  greatest 
effects.  What  concentration  of  dissolved  salts  is  necessary  in  order  that 
disintegrating  effects  shall  manifest  themselves  cannot  be  definitely 
stated.  This  is  a  field  problem  and  is  subject  to  wide  variations  under 
different  conditions. 

A  water  containing  relatively  little  dissolved  material,  acting  under 
favorable  conditions  of  porosity,  pressure  and  wide  temperature  changes 
upon  one  concrete,  may  accomplish  failure  of  the  structure;  while 
another  water,  of  high  saline  content,  meeting  a  dense,  impervious  con- 
crete, not  forced  through  the  mass  by  pressure  and  under  conditions  of 
small  temperature  change,  may  have  practically  no  action.  Manifestly, 
unless  these  varying  conditions  are  taken  into  account,  it  is  unscientific 
to  draw  any  conclusions  regarding  the  attack  of  different  waters  or  the 
resistivity  of  different  cements. 

It  may  be  laid  down  as  a  basic  principle,  however,  that  the  denser  a 
concrete,  other  conditions  being  equal,  the  greater  its  resistance  to  the 
attack  of  saline  waters  (10,  41,  57).  The  alkali  waters  of  the  Western 
states  have  given  a  great  deal  of  trouble  in  concrete  construction.  Most 
experimenters  conclude  that  their  action  upon  concrete  is  in  the  main 
mechanical  and  due  to  the  disruptive  force  of  crystallizing  or  efflorescing 
salts  deposited  in  the  pores  by  intermittent  submergence  and  drying 
out  (30,  38,  49,56). 

Of  course,  as  has  been  pointed  out,  action  of  this  sort  is  not  confined 
to  concrete,  and  any  material  of  construction  possessing  porosity  is 
liable  to  a  similar  disintegration.  The  remedy,  therefore,  is  to  prevent 
the  penetration  of  the  saline  solutions  by  the  employment  of  courses  of 
permanent,  impenetrable  materials,  preferably  asphaltic  layers. 

Where  the  attack  is  not  mechanical  but  chemical,  this  remedy  is  also 
applicable.  Unfortunately,  there  are  examples  of  construction  which 
are  exceptions,  and,  in  these,  some  change  in  the  chemical  or  mechanical 


214  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

constitution  of  the  cement  is  the  only  way  to  prevent  decomposition.  In 
concrete  block  construction,  where  the  blocks  may  be  made  long  before 
they  are  actually  put  into  the  structure,  it  is  found  of  great  advantage  to 
allow  them  to  harden  in  air  or  in  damp  sand,  and  so  permit  to  a  great 
extent  the  carbonation  of  the  lime  compounds.  Some  investigators  claim 
excellent  results  from  this  method  (41,  55). 

As  to  the  modifications  in  the  constitution  of  the  cement  that  will 
combat  the  action  of  saline  solutions,  there  is  a  great  disparity  of  opin- 
ion, which  possibly  is  based  upon  lack  of  standardization  of  experimental 
conditions.  It  is  generally  conceded  that  high  silica  cements  are  best 
suited  for  the  purpose  (7).  The  use  of  puzzolan  cements,  or  of  addi- 
tions of  puzzolan  to  the  cement  in  use,  is  also  well  recommended  (7,  37, 
66)  ;  and  the  addition  of  clay,  burnt  or  dehydrated,  finds  favor  with 
some  (7,  75).  As  to  the  lime  content  of  the  cement,  opinions  are  divided 
whether  it  should  be  high  (5,  41)  or  low  (92). 

Cement  of  greater  density  (57)  and  cement  ground  to  a  greater  fine- 
ness than  usual  (72)  are  favorably  commented  upon.  The  subject, 
because  of  its  great  complexity  and  because  of  the  questionable  value  of 
laboratory  results,  is  at  present  in  a  chaotic  state.  The  length  of  time 
that  must  elapse  before  judgment  may  be  passed  upon  the  permanence 
of  a  material  under  these  conditions  and  the  corresponding  newness  of 
the  field  of  Portland  cement  render  present  conclusions  largely  a  matter 
of  speculation. 

Effect  of  storage  in  various  saline  solutions  upon  the  strength  of 
mortar. — In  order  to  study  the  relative  resistance  to  saline  solutions 
offered  by  cements  varying  in  chemical  composition  and  in  fineness  of 
grinding,  a  series  of  132  2-inch  mortar  cubes  was  made  up,  in  the  pro- 
portion of  1:3,  with  standard  Ottawa  sand,  the  cements  used  being 

A.  A  high  silica  cement 

B.  A  low  silica  cement 

C.  A  cement  of  ordinary  composition,  sifted  and  remixed  so  that 

98.8  per  cent  passed  the  100  mesh  sieve  and  88.6  per  cent 
passed  the  200  mesh  sieve 

D.  The  same  cement  as  C  sifted  so  that  92  per  cent  passed  the 

100  sieve  and  75  per  cent  passed  the  200  sieve 


P  AC  IN  I,   METAMORPHISM    OF  PORTLAND    CEMENT 


215 


TABLE  24 
Analyses  of  the  Cements  Used  in  Tests  with  Saline  Solutions 


Per  cent 

A 

B 

c 

SiO2  

23.50 

19.74 

22.99 

Fe.Ov  . 

2.36 

2.75 

2.42 

A12O3  

7.28 

8.77 

6.79 

CaO 

62  18 

60  86 

60.84 

MgO. 

2  29 

2.86 

4.14 

SO3.                

1.11 

1.39 

1.76 

C02H2O,  alkalies  

1.28 

3.63 

1.06 

The  cubes  were  stored  24  hours  in  the  damp  closet,  and  then  trans- 
ferred to  the  solutions  mentioned  in  the  following  table,  three  cubes  to 
each  liquid,  and  there  stored  for  three  months,  then  broken. 

TABLE  25 

Comprcssive  Streiif/tli  of  Mortars  Stored  for  Three  Months  in  Various  Saline 

Solutions 

(Each  value  is  the  average  of  three  determinations) 


Storage  medium 

Pounds  per  square  inch 

High 

silica 

Gain, 
pei- 
cent 

Low 

silica 

Gain, 
per 
cent 

Finely 
ground 

Gain, 
per 
cent 

Coarsely 
ground' 

Gain, 
pei- 
cent 

1 

Croton  water 

2217 

9462 

2134 

2066 

Sodium          5% 

2267 

2 

2090 

-15 

3266 

53 

2273 

10 

sulphate,    10  % 

3264 

47 

2035 

-18 

2223 

4 

2262 

9 

Magnesium  5% 

3244 

46 

1787 

-28 

2233 

5 

2759 

33 

sulphate,    10$ 

2604 

18 

2646 

7 

3003 

42 

2489 

20 

Sodium          5  % 

2365 

7 

1785 

-28 

2305 

8 

2695 

30 

chloride,    10$ 

1778 

-20 

2019 

-18 

2968 

40 

2044 

-1 

Magnesium  5$ 

2331 

r 
•J 

1827 

-26 

2731 

33 

2305 

12 

chloride,    10$ 

1757 

O1 

1769 

-28 

2570 

20 

2269 

10 

Calcium        5  % 

2653 

19 

25169 

2 

2219 

4 

1808 

-13 

chloride,    10  %\     2224 

0 

1994 

-19 

2042 

-4 

2238 

8 

Average  gain 

(per  cent)    .  . 

10 

-17 

.... 

20 

12 

Average  of  two  determinations. 


216  .ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

The  general  deductions  from  these  experiments  for  the  period  covered 
are  that  the  high  silica  cement,  notwithstanding  its  slower  rate  of  har- 
dening, resists  the  action  of  these  dissolved  salts  better  than  the  low 
silica  cement,  and  the  finely  ground  cement  better  than  the  coarsely 
ground.  Moreover,  with  the  concentrations  used,  the  stronger  solutions 
in  nearly  every  case  had  a  more  destructive  effect  upon  the  strength  of 
the  mortar  than  the  weaker. 

The  strengths  here  obtained  by  storage  in  salt  solutions  are  in  general 
decidedly  greater  than  those  obtained  by  storage  in  fresh  water.  Ex- 
amination of  the  cubes,  when  removed  from  the  solutions  at  the  end  of 
the  test  period,  revealed  under  a  lens  that  the  exterior  was  being  at- 
tacked, minute  pittings  being  quite  distinct. 

The  strength  attained  by  these  specimens  may  be  considered  as  a  re- 
sultant of  the  balancing  of  two  effects :  the  deposition  of  crystallized  or 
precipitated  material  in  the  voids,  which  by  packing  the  spaces  with 
solids  will  increase  the  compressive  strength;  the  creation  of  additional 
voids  by  direct  solution  or  by  the  disruptive  effect  of  metathetically  pro- 
duced material.  It  is  probable  that  the  disintegrating  effect  for  these 
concentrations  is  reached  considerably  beyond  three  months'  exposure. 
From  the  increases  in  the  compressive  strength,  it  is  likely  that  at  this 
period  a  great  deal  of  crystallization  or  precipitation  has  proceeded, 
overbalancing  in  the  main  the  disruptive  effects.  This  is  a  general 
deduction,  and  single  instances  are  notable  in  which  the  reverse  holds 
good. 

In  the  case  of  the  finely  ground  cement,  the  density  of  the  mortar 
made  therefrom  has  prevented  the  disruptive  effect  to  a  greater  degree ; 
and  thus  the  deposition,  while  not  necessarily  as  much  as  in  the  coarser 
cement  mortars,  has  had  a  more  marked  effect  in  increasing  the  strength. 

Effect  of  storage  m  rock  water  upon  the  strenr/lli  of  lean  cement 
mortars. — A  series  of  briquettes  of  1 :  4  Ottawa  sand  mortars  was  made 
up,  using  a  normal  Portland  cement  of  high  quality.  The  mix  was  made, 
lean  purposely  to  accelerate  whatever  disintegrating  effect  might  occur. 
Batches  of  the  briquettes  were  stored  in  bottles  in  the  laboratory  for  the 
7-day  and  28-day  tests,  and  additional  series  were  stored  in  the  field,  for 
the  longer  tests,  at  stations  where  the  waters  in  question  were  encoun- 
tered. The  field  series  were  stored  in  running  water,  and  the  action 
upon  these  should  be  more  severe  than  upon  the  laboratory  specimens 
stored  in  still  water.  In  each  case  a  parallel  test  was  made  by  storing  a 
series  in  pure  drinking  water. 


PACINI,   METAMORPHISM   OF  PORTLAND   CEMENT 


217 


TABLE  26 
Tensile  Strength  of  1:4  Mortars,  stored  in  Rock  Water 


Water 

Strength,  pounds  per  square  inch 

Specimens 
in  average 

Stored  in  laboratory 

Stored  in  field 

7  days 

Gain 

28  days 

Gain 

3  mos. 

Gain 

6  mos. 

Gain 

Drinking.. 

«  \  5  J 

211 
220 

203 
221 

+4#' 

-4# 
+4$ 

297 

312 

287 
288 

320 

323 
313 
340 

"ijf 

-2# 
6£ 

324 

247 
303 
328 

12,12,6,6 
12,12,6,6 
12,12,6,6 
12,12,6,6 

5$ 

-3% 
-3fo 



-24f, 
-  Z% 
1% 

"B".  ... 

«  ^i>  > 

TABLE  27 
Analyses  of  Rock  Waters  in  Previous  Experiments 


Parts  per  million 

A 

B 

H2S.. 

44 

20 
7 
284 
124 
727 
826 
949 

15                4 
5                 4 
399               87 
118               38 
353               31 
546             270 
459             317 

SiO2  

Fe.203-fALA  
CaO  

MgO.... 

SO, 

Cl 

CO2   Alkalies,  etc  . 

Total  solids  

3037 

1895             751 

The  drinking  water  used  to  store  the  blanks  contained  in  neither  case 
more  than  100  parts  per  million  of  total  solids. 

The  most  consistent  reduction  of  strength,  although  a  slight  one,  is 
observed  in  the  case  of  water  B,  a  fairly  typical  sulphato-chloride  water 
according  to  Clarke's  classification  (18,  p.  190).  A  strikingly  high  and 
sudden  reduction  occurs  at  six  months  in  water  A,  a  sulphate  water 
charged  with  hydrogen  sulphide,  while  water  C,  a  chloride  water,  shows 
no  marked  reduction  of  the  strength,  which,  however,  may  be  due  to  a' 
low  salinity. 

The  six-month  briquettes  stored  in  water  A  showed  superficially  much 
minute  pitting,  due  to  the  removal  of  the  sand  grains,  presumably  by 
solution  of  the  matrix  of  the  cement.  Two  sections  were  cut  from  one 
of  these  briquettes,  one  transverse  and  one  longitudinal,  in  the  hope  of 
discovering  whether  any  replacement  of  the  original  material  by  sul- 


218  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

phates  or  sulphides  was  going  on.  The  microscopic  examination  did  not 
reveal  anything  of  the  sort,  the  sections  being  in  all  respects  similar  to 
sections  cut  from  the  briquettes  stored  in  drinking  water.  It  was  con- 
cluded therefore  that  the  loss  of  strength  was  due  to  actual  removal  of 
material  by  solution  rather  than  by  replacement  with  material  which 
would  cause  disintegration  through  a  discrepancy  in  volume. 

The  legitimate  general  deduction  from  these  tests  is  that,  over  the 
period  of  experiment,  the  effect  of  these  waters  is  greater  in  void  filling 
by  crystallization  or  precipitation  than  in  disintegration  by  solution  or 
disruption. 

The  void-filling  material,  if  of  a  stable  nature  and  not  likely  to  return 
into  solution,  should  be  in  a  measure  a  protection  against  the  further 
entrance  of  the  saline  solutions.  It  has  been  mentioned  that  this  prop- 
erty has  been  suggested  of  magnesium  hydroxide  (70).  Probably  upon 
this  possibility  is  based  the  reported  effect  of  chemically  inert  fine  ma- 
terials, added  to  the  cement  for  protection  against  such  destructive 
action. 

SUMMARY  OF  EXPERIMENTAL  EESULTS 

1.  Increase  of  temperature  of  the  water  with  which  cement  is  mixed 
causes  acceleration  of  the  set  up  to  a  certain  maximum  temperature, 
then  a  retardation. 

2.  Storage  in  cold  water,  without  freezing,  retards  the  hardening  of 
neat  cement,  and  that  of  mortars  more. 

3.  Increase  in  the  proportion  of  fine  particles  in  a  cement  decreases 
the  permeability  of  mortar  made  therefrom. 

4.  Mechanical  agitation  increases  the  strength  of  cement  up  to  a  cer- 
tain maximum  time;  after  which,  if  continued,  it  reduces  it. 

5.  The  setting  of  cement  is  accelerated  by  dryness  of  the  atmosphere. 

6.  An  excess  of  mixing  water  progressively  reduces  the  strength  of 
cement.     This  effect  is  partly  reversive  of  itself,  and  the  reversion  may 
be  increased  by  additional  colloidal  material  in  the  original  cement. 

7.  Water  percolating  through  concrete  dissolves  the  lime  of  the  ce- 
ment chiefly,  and  this  effect  tends  to  neutralize  itself  by  "healing." 

8.  Percolation  through  concrete  preferably  follows  the  bedding  planes. 

9.  Salts  in  solution  in  the  mixing  water  tend  to  lower  the  strength  of 
cement.    This  effect  may  be  neutralized  by  precipitation  in  the  pores. 

10.  Storage  in  saline  water  affects  low  silica  cements  more  than  it 
does  high  silica,  and  coarsely  ground  cements  more  than  it  does  finely 
ground  cements. 


PACINI,   METAMORPHISM    OF  PORTLAND    CEMENT  219 

GENERAL  CONCLUSIONS 

In  general,  the  metamorphism  of  Portland  cement  represents  on  an 
accelerated  scale  the  processes  which  occur  in  natural  rocks.  The  accel- 
eration is  of  course  due  to  the  ease  with  which  water  has  access  to  the 
finely  comminuted  particles  in  the  initial  stages  of  metamorphism.  Many 
of  the  minerals  found  in  natural  rocks,  when  ground  as  finely  as,  or  finer 
than  Portland  cement,  undergo  vastly  accelerated  reactions  in  the  pres- 
ence of  water;  colloidal  bodies  are  thereby  produced,  and  the  water  is 
rendered  alkaline  (18). 

The  end  product  of  prolonged  water  action  on  Portland  cement  bears 
a  striking  qualitative  similarity  to  the  end  product  in  the  kaolinization 
of  feldspars.  The  same  transformations  evidently  occur  in  both  cases, — 
the  alkalies  and  the  lime  are  abstracted,  and  the  water  and  alumina  con- 
tents increased.  The  exceeding  fineness  and  high  adsorptive  power  of 
the  resulting  products  are  also  similar.  The  action  of  water  on  nearly 
all  silicate  minerals  is,  in  effect,  a  repetition  of  this  process. 

The  peculiar  adsorptive  properties  of  colloidal  bodies  render  these 
liable  to  coagulation.  As  has  been  pointed  out  in  preceding  pages,  much 
of  the  cementing  material  of  conglomerates  and  sandstones,  except  where 
calcitic,  may  have  its  origin  in  a  similar  phenomenon. 

On  a  natural  scale,  the  action  of  water  is  greatly  retarded,  because  of 
the  larger  size  of  the  bodies  acted  upon,  and  the  consequent  paucity  of 
surface  upon  which  water  may  exert  its  influence.  When  Portland  ce- 
ment has  properly  undergone  its  initial  metamorphism,  the  setting 
process  being  complete  and  the  hardening  process  in  great  part  so,  it 
approaches  the  condition  of  a  natural  metamorphic  rock,  and  activities 
towards  its  further  change  are  katamorphic  and  vastly  slower  in  their 
results  than  the  initial  changes.  The  component  particles  have  now 
become  consolidated  and  the  surface  offered  to  the  action  of  water  is 
minimized.  Of  course,  this  is  truer  of  neat  cement  than  mortar  and 
truer  of  mortar  than  of  concrete,  these  being  in  the  order  of  increasing 
porosity. 

The  hypothesis  that  crystal  formation  is  responsible  for  the  strength 
of  hardened  cement  is  not  so  complete  and  satisfactory  as  the  colloidal 
hypothesis  just  referred  to.  In  a  compact  mass,  the  growth  of  crystals 
can  hardly  be  considered  anything  but  an  element  of  weakness.  As  has 
been  shown  by  the  foregoing  results,  the  effects  of  varying  some  of  the 
conditions  of  the  action  of  water  upon  cement  are  best  explained  by 
considering  the  hardening  a  coagulative  process  rather  than  a  process  of 
crystallization. 


220  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

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224:  ANNALS  NEW  YORK  ACADEMY  OF  SCIENCES 

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